Sintered Metal Filter Elements

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Sintered Metal Filter Elements Manufacturer

Sintered Metal Filter Elements OEM Variety Supplier

HENGKO is a reputable manufacturer and supplier known for producing top-quality Sintered Metal Filter Elements. With a strong commitment to excellence, HENGKO has established itself as one of the best in the industry. These filter elements are carefully crafted using advanced sintering techniques, resulting in a durable and efficient filtration solution.  

OEM Service 

Furthermore, HENGKO emphasizes customer satisfaction by providing personalized solutions and excellent customer support. We understand some unique requirements of each client and offer a comprehensive range of filter element sizes, shapes, and configurations to meet diverse filtration needs. 

If you are seeking a trusted manufacturer and supplier for high-quality Sintered Metal Filter Elements, HENGKO stands out as a leading choice, renowned for their exceptional products and commitment to delivering reliable filtration solutions.

OEM Special Sintered Metal Filter Elements Details : 

1.) By Materials :

You can choose from many kinds of metals and also some alloys to meet special requirements such as higher

temperature and pressure, corrosion resistance, etc 

   1. Stainless Steel sus316L, 316, 304L, 310, 347 and 430

   2. Bronze or Brass, we main supply Sintered Bronze Filters

   3. Inconel ® 600, 625 and 690 

   4. Nickel200 and Monel ® 400 (70 Ni-30 Cu)

   5. Titanium

   6. Others Metal Filter Materials Requires &#; Please Send  to Confirm.

2.) By Design Style :

  1.  Sintered Disc 

  2.  Sintered Tube 

  3.  Sintered Metal Filter Cartridge

  4.  Sintered Stainless Steel Plate

  5.  Sintered Porous Metal Sheet 

  6.  Sintered Cup  

   7.  Sintered Mesh Filter

If you are interested in customizing Sintered Metal Filters, please ensure that you confirm the following

specification requirements before placing an order. By doing so, we can recommend more suitable

sintered filters or sintered stainless steel filters or other options based on your needs.

The following requirements should be considered:

1. Pore size 

2. Micron rating 

3. Required flow rate  

4. Filter media to be used   

Types of S

intered Metal Filter Elements

Sintered metal filter elements are porous structures made from metal powders that are bonded together through sintering.
Normally offer a range of filtration capabilities and are widely used in various industrial applications.
Here are some of the main types of sintered metal filter elements:

By Craftsmanship

1. Sintered Wire Mesh Filters:

These filters are constructed by layering and sintering multiple sheets of metal wire mesh. They provide high strength, high permeability, and excellent resistance to high temperatures and pressures. Common applications include liquid and gas filtration, fluidization, and catalyst supports.

2. Sintered Metal Fiber Felt (Random Fiber) Filters:

These filters are made from randomly oriented metal fibers that are bonded together through sintering. They offer high porosity, high dust-holding capacity, and excellent filtration efficiency for fine particles. Common applications include air filtration, gas purification, and liquid filtration.

3. Sintered Powder Porous Metal Filters:

These filters are made from metal powders that are sintered into a porous structure. They provide high precision filtration, excellent chemical resistance, and the ability to filter very fine particles. Common applications include pharmaceutical and semiconductor processing, medical device manufacturing, and environmental protection.

4. Combination Filters:

These filters combine different types of sintered metal structures, such as wire mesh and fiber felt, to achieve specific filtration characteristics. They offer a tailored combination of strength, permeability, and filtration efficiency. Common applications include high-pressure filtration, multi-stage filtration, and specialized filtration processes.

By Materials:

Then if classification of sintered filter elements by metal material, we can check details as following:

1. Stainless steel sintered filters are made from stainless steel powder and offer high strength, corrosion resistance, and heat resistance.

They are commonly used in food and beverage processing, pharmaceutical, and chemical applications.

Stainless steel sintered filter

2. Bronze sintered filters are made from bronze powder and offer good wear resistance, corrosion resistance, and machinability.

They are commonly used in automotive, aerospace, and hydraulic applications.

Bronze sintered filter

3. Nickel sintered filters are made from nickel powder and offer high strength, corrosion resistance, and high-temperature resistance.

They are commonly used in aerospace, chemical, and nuclear applications.

Nickel sintered filter

Other metal sintered filters can also be manufactured from other metal materials, such as aluminum, titanium,

and molybdenum. These materials offer different properties to meet specific application needs.

In addition to these main types, there are various specialized sintered metal filter elements designed
for specific applications. These include pleated filters, basket filters, disc filters, and conical filters.

Main Features:

Sintered metal filter elements offer several advantages over other types of filters as following, including:

* High strength and durability
* Excellent resistance to corrosion and high temperatures
* High permeability and filtration efficiency
* Easy cleaning and regeneration
* Wide range of materials and pore sizes

Application

Sintered metal filter elements are used in a wide range of industries, including:

* Oil and gas
* Chemical processing
* Pharmaceuticals and electronics
* Food and beverage
* Water treatment and environmental protection
* Aerospace and automotive

The choice of sintered metal filter element depends on the specific application requirements,
such as filtration efficiency, pore size, operating temperature, and pressure.

Main features of our Sintered Metal Filter Elements

1. High Filtration Efficiency:

    As you know, Sintered metal filter elements are designed to provide excellent filtration efficiency by effectively removing solid particles and contaminants from fluids or gases. They can achieve filtration levels ranging from coarse to fine, depending on the specific application requirements. 

2. Robust Construction:

    These filter elements are made from sintered metal powders, typically stainless steel, which ensures their durability and resistance to corrosion, high temperatures, and pressure differentials. They can withstand harsh operating conditions and maintain their filtration performance over an extended service life.

3. Uniform Pore Structure:

    Sintering involves bonding metal particles together, creating a porous structure with precisely controlled pore sizes. Top-quality sintered metal filters have a uniform pore structure, enabling consistent and reliable filtration performance.

4. Wide Chemical Compatibility:

    Sintered metal filter elements are chemically inert and compatible with a broad range of fluids and gases. They can effectively filter various liquids, acids, alkalis, solvents, and gases without undergoing degradation or chemical reaction.

5. High Flow Rates:

    The design of sintered metal filters allows for high flow rates while maintaining efficient particle removal. They offer low-pressure drops, minimizing energy consumption and maximizing filtration throughput.

If you are looking for more details, kindly visit Fine Pore Porous Metal Components Manufacturer.

6. Excellent Cleanability:

    Sintered metal filter elements can be easily cleaned through backwashing, ultrasonic cleaning, or chemical cleaning methods. Their robust construction and stable pore structure enable repeated cleaning cycles without compromising filtration performance.

7. Wide Temperature and Pressure Range:

    HENGKO's filters can withstand high operating temperatures and pressure differentials. They are suitable for applications requiring filtration in extreme temperature conditions or under high-pressure environments.

8. Versatility:

    Sintered metal filter elements find applications in various industries, including chemical processing, pharmaceuticals, food and beverage, oil and gas, water treatment, automotive, and aerospace. They are adaptable to different filtration needs, offering customized options for specific applications.

9. Low Maintenance:

   Due to their durability and cleanability, sintered metal filters require minimal maintenance. Regular cleaning and occasional replacement ensure their long-term reliability and efficient filtration performance.

10. Consistent Performance:

     Top-quality sintered metal filter elements undergo rigorous quality control measures during manufacturing to ensure consistent performance and adherence to filtration standards. 

Applications of Sintered Porous Metal Filter Elements 

Sintered porous metal filter elements find a wide range of applications across various industries due to their unique characteristics and filtration capabilities. Here, I will provide a detailed explanation of some key applications: 

1. Filtration in the Chemical Industry:

    Sintered porous metal filter elements are extensively used in the chemical industry for filtration processes. They can effectively remove solid particles, contaminants, and impurities from liquids and gases. In chemical manufacturing, these filters are employed in processes such as catalyst recovery, polymer production, and separation of different chemical compounds. Their robust construction and chemical compatibility make them suitable for filtering aggressive chemicals and corrosive substances.

2. Filtration in the Pharmaceutical Industry:

    In the pharmaceutical industry, sintered porous metal filters play a vital role in ensuring the purity and quality of drugs and pharmaceutical products. They are commonly used for sterile filtration, removing bacteria, particles, and microorganisms from liquids, gases, and solvents. These filters are crucial in pharmaceutical processes like fermentation, purification of active pharmaceutical ingredients (APIs), and filtration of pharmaceutical intermediates. Their high filtration efficiency and cleanability help maintain strict quality standards and prevent contamination.

3. Filtration in the Food and Beverage Industry:

    Sintered metal filters are widely employed in the food and beverage industry for various filtration applications. They are used for clarifying liquids, removing solids, and ensuring product quality and safety. These filters are utilized in processes such as beer and wine filtration, vegetable oil purification, dairy product processing, and juice clarification. Sintered metal filter elements provide hygienic filtration, high flow rates, and resistance to high temperatures and pressures, making them suitable for demanding food and beverage production environments.

4. Filtration in the Oil and Gas Industry:

    Sintered porous metal filters find extensive use in the oil and gas industry for filtration and separation purposes. They are employed in upstream exploration and production activities, as well as downstream refining and processing operations. These filters are utilized for removing particulate matter, sediments, and contaminants from oil, gas, and various process fluids. They offer excellent resistance to high pressures, temperature fluctuations, and aggressive chemicals, making them well-suited for critical applications such as well injection, natural gas filtration, and hydrocarbon recovery.

5. Filtration in the Water Treatment Industry:

    Sintered metal filter elements play a crucial role in the water treatment industry, providing efficient filtration for both potable water and wastewater treatment processes. These filters effectively remove suspended solids, sediments, bacteria, and other impurities from water, ensuring clean and safe drinking water or meeting stringent discharge standards for wastewater. Sintered metal filters are utilized in applications such as pre-filtration, membrane protection, activated carbon filtration, and groundwater remediation. Their long service life, cleanability, and resistance to fouling make them ideal for continuous filtration operations.

6. Filtration in the Automotive Industry:

    Sintered porous metal filter elements are employed in various applications within the automotive industry. They are commonly used for air filtration in automotive engines, ensuring clean intake air and protecting the engine from contaminants. Sintered metal filters can efficiently capture particulate matter, dust, and other airborne impurities, preventing engine damage and maintaining optimal performance. Additionally, these filters are utilized in fuel filtration systems, providing effective particle removal and preventing fuel injector clogging.

7. Filtration in the Aerospace Industry:

    In the aerospace industry, sintered metal filters are utilized for critical filtration applications, ensuring the reliability and performance of aerospace systems. These filters are used in hydraulic systems, fuel systems, lubrication systems, and pneumatic systems. They provide efficient particle removal, protecting sensitive components from contamination and maintaining system integrity. Sintered metal filters are valued for their high temperature resistance, chemical compatibility, and ability to withstand extreme operating conditions, making them suitable for aerospace applications.

Sintered porous metal filter elements offer versatile and reliable filtration solutions across a wide range of industries. Their robust construction, high filtration efficiency, chemical compatibility, and resistance to harsh conditions make them indispensable in various critical applications, ensuring the purity, quality, and safety of products and processes.

What you should care when OEM for your filtration project or devices , equipment ? 

When opting for OEM (Original Equipment Manufacturer) services for your filtration project or devices, there are several key aspects to consider. Here are some important factors to care for during the OEM process:

1. Quality Assurance: Ensure that the OEM provider has a strong commitment to quality assurance. Look for certifications, such as ISO , that demonstrate their adherence to international quality standards. Quality is crucial in filtration applications to ensure reliable and consistent performance.

2. Customization Capabilities: Evaluate the OEM provider's ability to customize filtration solutions according to your specific project requirements. Discuss your application needs, such as desired filtration efficiency, flow rates, pressure limits, and chemical compatibility. A capable OEM partner should have the expertise to design and manufacture tailored filtration equipment that aligns with your unique specifications.

3. Technical Expertise: Consider the OEM provider's technical expertise and experience in filtration technology. They should have a deep understanding of filtration principles, materials, and industry best practices. Look for a track record of successful filtration projects and a team of skilled engineers who can provide expert guidance and support throughout the OEM process.

4. Product Range and Innovation: Assess the OEM provider's product range and their commitment to innovation. A diverse range of filtration products indicates their capability to address various filtration challenges. Additionally, inquire about their research and development efforts to ensure they stay updated with emerging technologies and can offer cutting-edge solutions for your project.

5. Manufacturing Facilities: Evaluate the OEM provider's manufacturing facilities and capabilities. Consider factors such as production capacity, equipment quality, and quality control processes. A well-equipped manufacturing facility ensures efficient production, timely delivery, and consistent product quality.

6. Regulatory Compliance: Verify that the OEM provider follows relevant industry standards and regulations. Depending on your application and industry, there may be specific compliance requirements, such as FDA regulations for food and pharmaceutical filtration. Ensuring compliance with applicable standards and regulations is essential to meet legal obligations and ensure product safety and reliability.

7. Customer Support and Service: Assess the OEM provider's commitment to customer support and after-sales service. They should offer responsive communication channels, technical assistance, and warranty support. Timely and reliable customer support is crucial in addressing any concerns or issues that may arise during the OEM process or after product deployment.

8. Cost-effectiveness: While considering the above factors, also evaluate the OEM provider's pricing and cost-effectiveness. It's important to strike a balance between quality, customization, and affordability. Request detailed quotations and compare them with the value and benefits offered by the OEM provider to make an informed decision.

By considering these key factors during the OEM process for your filtration project or devices, you can ensure a successful partnership with an OEM provider that meets your specific requirements, delivers high-quality products, and provides excellent support and service.

FAQs 

Q1: What are the key features of sintered metal filter elements?

       A1: Sintered metal filter elements possess several key features that make them highly effective in filtration applications.

            These features include high filtration efficiency, robust construction for durability and resistance to corrosion and high temperatures, uniform pore structure for consistent performance, wide chemical compatibility, high flow rates, excellent cleanability, suitability for a wide temperature and pressure range, versatility across industries, low maintenance requirements, and consistent performance.

Q2: What are the common applications of sintered metal filter elements?

       A2: Sintered metal filter elements find applications in various industries.

            Some common applications include filtration in the chemical industry for catalyst recovery and separation processes, filtration in the pharmaceutical industry for sterile filtration and drug purity maintenance, filtration in the food and beverage industry for clarifying liquids and ensuring product quality, filtration in the oil and gas industry for removing contaminants from oil, gas, and process fluids, filtration in the water treatment industry for purifying potable water and treating wastewater, filtration in the automotive industry for air and fuel filtration, and filtration in the aerospace industry for critical filtration in hydraulic, fuel, and lubrication systems.

Q3: How do sintered metal filter elements function?

       A3: Sintered metal filter elements function based on their unique structure.

            They consist of metal powders that are bonded together through the sintering process, creating a porous structure with controlled pore sizes. When a fluid or gas passes through the filter, particles larger than the pore size get trapped, while the fluid or gas passes through the filter media.

            The uniform pore structure ensures consistent filtration performance, and the high filtration efficiency removes solid particles and contaminants from the fluid or gas stream.

Q4: What is the installation process for sintered metal filter elements?   

       A4: The installation process for sintered metal filter elements may vary depending on the specific application and the design of the filter housing. In general, the filter element needs to be securely installed in the appropriate housing or filter assembly. This typically involves ensuring proper alignment and sealing to prevent bypass of the fluid or gas being filtered.

             It's important to follow the manufacturer's instructions and guidelines for the specific filter element and housing being used to ensure a correct and effective installation.

Q5: How can sintered metal filter elements be cleaned?

       A5: Sintered metal filter elements can be cleaned through various methods such as backwashing, ultrasonic cleaning, or chemical cleaning. Backwashing involves reversing the flow through the filter to dislodge and remove trapped particles. Ultrasonic cleaning uses high-frequency sound waves to agitate and remove contaminants from the filter surface.

            Chemical cleaning involves using specific cleaning agents to dissolve or remove accumulated debris or substances from the filter. The appropriate cleaning method will depend on the type of contaminants and the specific requirements of the filter element, and it's important to follow the manufacturer's recommendations for cleaning procedures.

Q6: How long do sintered metal filter elements last?

       A6: The lifespan of sintered metal filter elements can vary depending on factors such as the operating conditions, the type and concentration of contaminants, and the maintenance practices. However, with proper care and regular cleaning, sintered metal filter elements can have a long service life.

            The robust construction and cleanability of these filters allow for repeated cleaning cycles, which helps maintain their filtration performance and extends their lifespan. It's recommended to monitor the filter element's condition regularly and replace it when it shows signs of damage or reduced filtration efficiency.

Q7: Can sintered metal filter elements be customized for specific applications?

        A7: Yes, sintered metal filter elements can be customized to suit specific application requirements. The pore size, dimensions, and shape of the filter element can be tailored to meet the desired filtration specifications. Additionally, the choice of material, such as stainless steel or other alloys, can be selected based on the chemical compatibility and temperature resistance needed for the application. Manufacturers often offer customization options to ensure the filter element's optimal performance in specific industries and applications.

Q8: Are there any safety considerations when using sintered metal filter elements?

      A8: When using sintered metal filter elements, it's important to consider the specific safety requirements of the application and industry. Depending on the substances being filtered, proper safety measures should be implemented, such as providing adequate ventilation, using appropriate personal protective equipment (PPE), and following established safety protocols. It's crucial to understand the chemical compatibility, temperature limits, and pressure ratings of the filter element to ensure safe and reliable operation.

These comprehensive answers to frequently asked questions provide a deeper understanding of sintered metal filter elements, their features, applications, function, installation, cleaning, lifespan, customization options, and safety considerations.

For further inquiries or to get in touch with HENGKO, please feel free to contact us via at .

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Most commonly, implants are fixed in place with the help of bone cement or metal screws. However, the major drawback to bone cement is fragmentation which can result in foreign body response to the released debris; this mode of implant fixation usually leads to periprosthetic osteolysis, early aseptic loosening, and failure of the implant [48]. For quicker healing after implantation, osseointegration is critical. Osseointegration, meaning, bone tissue ingrowth into the implant surface. The correlation between the morphology and size of the porous surface and the strength of fixation with the surrounding tissue has also been determined [49]. Many studies have concluded that open porosity improves implant wettability and aids bodily fluids flow, thus improving osseointegration when >100 μm pore size is present [50]. The porosity is either homogeneously or non-homogeneously distributed based on the processing method. Discussed are several fabrication methods for producing open-cell porous implants or coatings.

2.2.1. Sintering.

Sintering is one of the oldest and most evolved techniques in powder metallurgy for producing density-controlled materials. The basic concept of the process is to prepare powder (metal/ceramics) by compacting and binding powdered raw material and providing thermal energy for the compacted powder for densification and grain growth. In this process, the powder particles bond at high temperatures with minor changes to the initial powder particle shape. Binders hold the powder particles together, providing enough area for mass transport during solid-state diffusion. Due to this technique&#;s highly evolved nature, many studies on porous orthopedic implant structures have employed sintering or modified versions of sintering for preparing porous metal structures.

The porosity of the sintered structures can be controlled by tailoring the shape and size of the metal powder, the compaction pressure, and the temperature and time of sintering. It was observed that the compaction pressure and the sintering temperature significantly impact the microstructural and mechanical properties of the porous sintered metals. In general, it was observed that sintered Ti compacts at K, K, and K at no applied pressure; as the temperature increased, the porosity decreased. However, the porosity remained more significant than 30% for each temperature, and almost 100% was observed to be open porosity. Moreover, the effect of different applied pressures at different sintering temperatures has also been studied, and it was observed that the porosity decreases considerably (&#;19%). However, most of the porosity still was found to be open porosity. The scanning electron microscope (SEM) images of the microstructure of Ti compacts sintered at K, K, and K with an applied pressure of 10 MPa can be seen in figures (a)&#;(c), respectively [51].

Additional investigations produced porous functionally graded Ti using the sintering method by stacking layers of powders with varying particle sizes and the volume fraction of the additive (silicon), i.e. the low volume fraction of additive with finer powder (20% with 45 μm) to the high-volume fraction of additive with coarser powder (45% with 200 μm). The cross-sectional microstructure of a functionally graded porous Ti structure prepared in this manner is shown in figure (d) [45].

Another alternative form of porous surface characteristics to implant the structure&#;s dense core via sintering is metal fibers instead of metal powder. This method has been investigated for both stainless steel and Ti fibers, and the procedure used to make such porous coatings is similar to the powder metal sintering process [53&#;56]. The metal fibers are laid complying with the form of the implant structure, compacted, and then sintered at high temperatures. The solid-state diffusion process forms a fully interconnected porous coating at each point of contact of the fibers [57]. However, the main drawback of this process is that compacting the metal fibers to the form of the implant structure is challenging and time-consuming. Moreover, the interfacial bond between the dense implant core and the fiber mesh coating depends on the complexity of the contours of the implant structure [53]. Even though the sintering method of building porous structures is relatively mature, several limitations exist. A most relevant limitation is that particle oxidation could inhibit the proper bonding of the particles because it is a high-temperature operation. Further, solid-state diffusion bonding of particles usually results in the neck formation comprised of brittle phases and might result in lower mechanical toughness and fatigue resistance. Moreover, the pore size and morphology are usually irregular and largely dependent on the particle size and shape. However, these limitations could be substantially improved upon by using appropriate sintering techniques [13].

Many modified sintering techniques have been investigated to produce porous metallic structures with improved porosity and controlled pore morphology, including the space holder, the spark plasma sintering (SPS), and the replication methods. In the space holder method, several investigations have used carbamide particles as the space holder in preparing porous Ti and porous Ti6Al4V alloys. Carbamide has been chosen in the space holder method because of its ideal spherical particle geometry and chemical properties, such as ease of removal before sintering [58, 59]. A properly sieved and sized mixture of Ti or Ti6Al4V with carbamide was weighed and compacted under pressure. The compaction was then heat treated so that the carbamide particles dissociated at lower temperatures (&#;193 °C), and the dissociated by-products were expelled by either using a vacuum furnace or by the continued flow of argon. Thereby, the heat treatment cycle was typically followed where the compact was first heated up to 100 °C, and then slower heating rates were used up to 500 °C to ensure enough time for most of the carbamide particles to dissociate, and the consequent by-products were expelled. Following this, much faster heating rates could be used up to the sintering temperature at which the compaction was held for a considerable time, depending on the size of the compaction being sintered [58]. In this method, the size, shape of the pores, and porosity could be controlled primarily by controlling the volume fraction and the shape of the space holder particles. Other parameters that determine the porosity and the pore morphology are the compaction pressure and the holding time during sintering. While the compaction pressure applied to prepare the pre-sintered compact varied between investigations, the dependence on the mean porosity and mechanical properties (such as yield strength) and the compaction pressure seemed similar, i.e. as the compaction pressure increased, the mean porosity decreased. Also, it was observed among several investigations that the porosities that could be produced by this method ranged between 55% and 75%. It was observed that most of the pores were considered to possess consecutive and open cell morphology, with the sizes of the majority of these pores (<700 μm) being less than the largest space holder particle size (&#;700 μm). The pores with larger sizes were observed to be the consequence of pore coalescence. Furthermore, the pore walls&#; thickness is believed to significantly impact the porous structure&#;s mechanical strength. Thereby, it has been observed that, while the pore wall thickness of the structure produced by this method is in the same range as any other powder metallurgy process (i.e. &#;100&#;200 μm; compared with Berger&#;s report), interconnected angular-shaped micropores were observed along the pore walls suggesting that the sintering process was incomplete because of low diffusivity. While these micropores were considered beneficial in improving the interconnectivity of the pores, they might significantly deteriorate the structure&#;s mechanical properties. Different space holders or compaction techniques investigated other variants of this process [60, 61].

Another variant of the sintering technique is the SPS method. SPS or field assisted sintering technique (FAST) is a process similar to hot pressing where the heat required to sinter the powder particles in a compact is provided by joule heating due to the current flowing within the compact [62]. The general working principle of SPS, as indicated by figure (a), is that the sintering powder is compacted within a graphite die and DC voltage pulses pass through the die, and the compact (in the case of conductive sintering powder) produces joule heating, with heating rates up to °C·min&#;1, cooling rates of up to 400 °C·min&#;1 and maximum temperature of °C, sintering conditions could be facilitated by appropriately controlling the pulse voltages and durations [63]. Furthermore, this process could be controlled by controlling the die&#;s measured temperature, power, or current. The rapid heating and cooling rates make this one of the fastest sintering processes, thereby ensuring limited grain growth in the sintered metal [64].

The powder mixture is produced similarly to the space holder technique to produce porous metal structures using the SPS technique. The metal or alloy powder is mixed with varying volume fractions of space holder constituents such as NaCl or NH4HCO3. Then, the powder mixture is cold compacted under pressure to produce green compacts, sintered using SPS in a specially designed graphite die, as shown in figure (b) [65]. In the case of the study, where NaCl was used as an additive, post-sintering dissolution of NaCl in deionized water produced porous Ti6Al4V structures [66]. And in the case of the study where NH4HCO3 was used as an additive, it dissociates into NH3, H2O, and CO2 and is expelled during the sintering process and thus produces porous Ti structures [65]. In both studies, the x-ray diffraction (XRD) analysis of the porous structure showed negligible impurity content indicating that the space holders used were eliminated during the process. Also, it was observed that the majority phase appears to be α-Ti in the post-sintered structure, and the grains developed in the sintered porous structure are mostly fine. This indicates that the SPS process offers extremely fast heating and cooling rates.

The porosity, pore size, and morphology of the porous structures produced by the SPS method showed similarity with the previously discussed space holder method. In general, two types of pores were observed: Macro pores caused due to the dissociation of the space holder, and the micropores, within the pore walls of the macro pores, caused because of the incomplete sintering between adjacent metal particles (as shown in figures (c) and (e) in both the studies). Both studies also observed that as the sintering temperature was increased or by heat treatment post-sintering, the pore walls became thicker, and the porosity reduced (as shown in figures (d) and (f) in both studies). Also, both studies produced 40%&#;70% porosities; most pores were well interconnected.

Finally, the replication method&#;s third variant of the sintering method is discussed here. This process is typically three-step and has traditionally been used to prepare porous ceramics [13]. However, some investigations have used this method to produce porous Ti and Ti alloys. This method immersed polyurethane foams in a slurry and then rapidly dried for the metal powder to positively maintain the polyurethane foam replica. The slurry comprises 70% by weight Ti6Al4V and 20% by weight H2O and ammonia solution, where the ammonia solution has been added to improve the flow properties of the slurry. After repeating this process multiple times till the polyurethane foam struts were coated entirely with the Ti6Al4V powder, the polyurethane foam and binder were removed thermally, and the remaining Ti6Al4V powder arrangement was sintered, forming an open-cell reticulated Ti6Al4V foam [67]. This three-step process&#;s schematic is shown in figure (a) [13].

As expected, in this process, the flowability of the slurry, controlled via particle size distribution, binder chemistry, the pH of the slurry, air bubble quantity, and the solid&#;liquid ratio, determines the quality of foam produced by this process [68]. By this process, Ti alloy foams of 88% primarily open porosity have been attained, and the pore morphology could be observed in the SEM image shown in figure (b) [67]. The pores formed are chiefly found to be of three types: the primary porosity, comprising of smaller pores on the strut surface; secondary porosity, medium-sized pores formed at the core of the hollow strut formed by previously occupied polyurethane foam; and the tertiary porosity, larger open pores between the struts. A subsequent study observed that a second coating of the powder slurry and second sintering on a previously sintered foam enhanced the density and mechanical properties of the Ti or Ti alloy foams [69].

Even though sintering is a very mature metallurgical process, up to 80% of porosities could be achieved with slight modification. However, the process has inherent limitations. Sintered porous metallic structures are susceptible to brittle fracture and low fatigue resistance. Since, in this process, the metal particles bond via a solid-state diffusion process, the neck formed between metal particles after sintering is usually quite brittle. Also, the sintering process usually produces non-homogeneous pore distribution and pore morphology.

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