Powder Metallurgical Techniques Research Articles

The Role of Foaming Agent and Processing Route in the Mechanical Performance of Fabricated Aluminum Foams

The results of the present study highlight the role of foaming agent and processing route in influencing the contamination of cell wall material by side products, which, in turn, affect the macroscopic mechanical response of closed-cell Al-foams. Several kinds of Al-foams have been produced with pure Al by the Alporas melt process and powder metallurgical technique, all performed either with conventional TiH2 foaming agent or CaCO3 as an alternative. Mechanical characteristics of contaminating products induced by processing additives, all of which were presented in one or another kind of Al-foam, have been determined in indentation experiments. Damage behavior of these contaminations affects the micro-mechanism of deformation and favors either plastic buckling or brittle failure of the cell walls. It is justified that there is no discrepancy between experimental values of compressive strengths for Al-foams comprising ductile Al + Al4Ca eutectic domains and those prescribed by theoretical models for closed-cell structure. However, the presence of low ductile Al + Al3Ti + Al4Ca eutectic domains and brittle particles/layers of Al3Ti, fine CaCO3/CaO particles, Al2O3 oxide network, and, especially, residues of partially reacted TiH2, results in reducing the compressive strength to values close to or even below those of open-cell foams of the same relative density.

High-temperature oxidation resistance and magnetic properties of Si-doped Sm2Co17-type magnets at 500 °C

The high-temperature oxidation resistance and magnetic properties of Si-doped Sm2Co17-type magnets at 500°C were systematically investigated. The Sm(Co0.76, Fe0.1, Cu0.1, Zr0.04)7Six (x=0–0.6) magnets were prepared by the conventional powder metallurgical technique. It is found that the addition of silicon in the Sm2Co17-type magnet can remarkably improve its oxidation resistance. Moreover, a small amount of silicon addition can also increase its high-temperature intrinsic coercivity. A maximum intrinsic coercivity of 6.7kOe at 500°C was obtained for the Sm2Co17-type magnet with Si content x=0.4, whose high-temperature maximum energy product loss was about 2.5 times smaller than pure Sm2Co17-type magnet after oxidation at 500°C for 100h, indicating the enhanced oxidation resistance. Its corresponding Curie temperature and saturation magnetization are about 723.9°C and 7.4kG, respectively.

On the Possibility of Occurrence of Anisotropy in Processing of Cu-CNT Composites by Powder Metallurgical Techniques

Copper - multiwall carbon nanotubes (MWCNT) composite was processed by powder metallurgical processing technique. Pure copper powder and MWCNT were mechanically alloyed by high energy milling to produce Cu-MWCNT composite powder. The composite powder was subsequently consolidated by vacuum hot pressing. Characterization studies were conducted along axial (hot pressing direction) and radial (transverse) directions. Microstructural observations of the processed composite revealed random distribution of MWCNT in axial direction and aligned distribution in radial direction. The structure property correlation was established and it revealed certain degree of anisotropy in mechanical and electrical properties of the composite.

The mechanism of enhanced magnetic properties of sintered permanent magnets by substitution of Pr for Nd

In this study, the influence of substitution of Nd with Pr on the magnetic of sintered permanent magnets was investigated. The samples were prepared by traditional powder metallurgical technique. The nominal composition of the alloys is (Nd 1− x Pr x ) 29Dy 1.3R 3.1Fe bal (R = Al 0.3Cu 0.2 Co 1.5 B 1Zr 0.1, wt%) with x varying from 0 to 1 in steps of 0.2. Experimental results show that the overall magnetic properties, especially the intrinsic coercivity and thermal stability of the magnets, could be improved by substituting Nd with Pr in the magnets. When the Pr replaces all Nd in the magnets, excellent performance magnets with Br = 13.65 KGs, Hcj = 22.13 KOe, (BH) max = 46.1 MGsOe are obtained with a low Dy content (1.3 wt%).

Microstructural evolution during mechanical milling of Ti/Al powder mixture and production of intermetallic TiAl cathode target

Titanium aluminides are of great technological interest because of their attractive mechanical properties. Mechanical milling/alloying is a promising powder metallurgical technique, which can achieve ultrafine, uniform and manipulable microstructures. In this study, we employed a recently revisited discus mill to produce a composite Ti–(50–57) at.%Al powder feedstock, which is suitable for hot consolidation to produce bulk cathode targets for physical vapour deposition (PVD) coatings. The effects of milling time, quantity of process control agent (PCA) and discus-to-powder weight ratio (DPR) on the microstructure evolution of the attendant Ti/Al composite powder were investigated in detail. It was found that to produce Ti/Al composite powders with a fine particle size and a uniform microstructure, the practicable processing parameters should be 2 or 3% isopropanol addition as PCA, 12 h of milling time and at least 13:1 DPR weight ratio. Cathode targets were produced by hot isostatic pressing (HIPing) the as-milled powders. The targets were then used to produce a PVD TiAlN coating which had an average microhardness of 2400 HV.

Structural and Material Design of Open‐Cell Powder Metallurgical Foams

AbstractHigh porosity permeable materials have been manufactured on the basis of the highly uniform structure of foamed polyurethane since the 1950 s. This paper shows the development of open cell foams based on all kinds of steels, titanium alloys, and also open‐cell molybdenum foams made by a powder metallurgical replication technique. Such materials show a wide range of physical and mechanical properties, which may be adapted to various requirements. The automotive industry, for example, needs high‐temperature resistant materials with high permeability and good strength for catalytic conversion. For orthopaedic implants, the network‐like metal foams made of titanium, tantalum, or steel exhibit a bone‐like structure. The powder metallurgical replication route represents an economic method to process open‐cell metal foams with a unique combination of properties for a wide range of applications.

Carbon as a sacrificial alloying element in processing Fe-P soft magnetic alloys

The present investigation deals with designing Fe-P based binary alloy produced by in-house developed powder metallurgical technique based on ‘Hot Powder Preform Forging’. Proper soaking of preforms at high temperature (1050°C) eliminates iron-phosphide eutectic and brings entire phosphorus into solution in iron. Attempting hot forging thereafter completely eliminates hot as well as cold shortness and thereby helps to form these preforms into very thin sheets of 0.5mm. The use of costly hydrogen atmosphere during sintering has been eliminated by use of addition of carbon. The glassy ceramic coating applied over the compact serves as a protective coating to avoid atmospheric oxygen attack over the compact held at high temperature. The alloy so formed was subjected to density examination at various stages. Microstructural study has been carried out to estimate the grain size, volume percentage porosity in the alloy and uniform distribution of phosphorus in iron matrix. Fe-0.07wt% C-0.3wt% P alloy so formed yielded coercivity as low as 0.45 Oe, resistivity as high as 17.4 μΩcm and total loss as low as 0.176 W/Kg. The alloy which is drawn to thin sheets could find its possible application in manufacturing transformer cores.

Design and development of powder processed Fe–P based alloys

The present investigation deals with designing Fe, Fe–P binary and Fe–P–Si ternary alloys produced by an in-house developed powder metallurgical technique based on ‘Hot Powder Preform Forging’. Proper soaking of preforms at high temperature (1050 °C) eliminates iron-phosphide eutectic and brings entire phosphorus into solution in iron. Attempting hot forging thereafter completely eliminates hot as well as cold shortness and thereby helps to form these preforms (alloys) into very thin sheets of 0.5 mm. The use of costly hydrogen atmosphere during sintering has been eliminated by the addition of carbon as a reducing agent to form CO gas within the compact by reacting with oxygen of iron powder particles. The glassy ceramic coating applied over the compact serves as a protective coating to avoid atmospheric oxygen attack over the compact held at high temperature. These alloys so formed were subjected to density examination at various stages. Microstructural study has been carried out to estimate the grain size, volume percentage of porosity in the alloys, and uniform distribution of phosphorus and silicon in an iron matrix. X-ray diffraction studies of these alloys revealed the presence of only ferrite as product phase. Addition of alloying elements such as P and Si has improved the resistivity and magnetic properties of iron. Fe–0.07C–0.2O–0.3P–0.5Si alloy showed a resistivity as high as 31.7 μΩ cm. Coercivity values of the alloys ranged from 0.51 to 1.98 Oe. The total magnetic loss of Fe–0.07C–0.2O–0.3P–0.5Si alloy was the lowest (2.03 W/kg) amongst the alloys developed owing to its high resistivity combined with its low coercivity. These alloys which are drawn to thin sheets could find their possible application in the manufacturing of transformer cores.

Characterization of Ti–6Al–4V alloy foams synthesized by space holder technique

Ti–6Al–4V foams, biomedical candidate materials, were synthesized by powder metallurgical space holder technique as a result of evaporation of magnesium to achieve desired porosity content. Final products contained porosities in the range ∼43–64% with an average macropore size between 485 and 572 μm and a lamellar type Widmanstätten microstructure composed of α-platelets and β-laths. Unlike the case of bulk Ti–6Al–4V alloy tested under compression loading, compression stress–strain curves of manufactured Ti–6Al–4V foams were similar to those of elastic–plastic foams, which contain a linear elastic region; a plateau stage; and a densification stage. In the plateau region deformation bands perpendicular to the compression axis were developed and cell collapsing took place together with the buckling and fracture of some of the cell walls and edges in a ductile manner. Calculated elastic modulus and yield strength were in the range 1.42–14.7 GPa and 28.2–150 MPa, respectively, and the foam mechanical properties were found to be dependent on micro porous cell wall properties, which in turn depends on neck size between powder particles. Around 330 MPa yield strength value was calculated for porous cell walls by the use of Ti–6Al–4V alloy powder samples sintered in loose and compacted conditions, which were utilized to simulate the cell wall structure of foams. In addition, overall mechanical properties of foams were investigated considering macro porosity fraction, p macro, and the yield strength of foams exhibited a power law dependence, similar to commonly used minimum solid area models, in the form of A * (1 − p macro) n , where the proportionality constant “ A” was found to be the yield strength of micro porous cell walls.

Fabrication and characterization copper/diamond composites for heat sink application using powder metallurgy

Copper composites reinforced with diamond particles were fabricated by the powder metallurgical technique. Copper matrix and diamond powders were mixed mechanically, cold com- pacted at 100 bar then sintered at 900?C. The prepared powders and sintered copper/diamond composites were investigated using X-ray diffraction (XRD) and scanning electron microscope equipped with an energy dispersive X-ray analysis (SEM/EDS). The effect of diamond contents in the Cu/diamond composite on the different properties of the composite was studied. On fracture surfaces of the Cu/uncoated diamond composites, it was found that there is a very weak bonding between diamonds and pure copper matrix. In order to improve the bonding strength between copper and the reinforcement, diamond particles were electroless coated with NiWB alloy. The results show that coated diamond particles distribute uniformly in copper composite and the interface between diamond particles and Cu matrix is clear and well bonded due to the formation of a thin layer from WB2, Ni3B, and BC2 between Cu and diamond interfaces. The properties of the composites materials using coated powder, such as hardness, transverse rupture strength, thermal conductivity, and coefficient of thermal expansion (CTE) were exhibit greater values than that of the composites using uncoated diamond powder. Additionally, the results reveals that the maximum diamond incorporation was attained at 20 Vf%. Actually, Cu/20 Vf% coated diamond com- posite yields a high thermal conductivity of 430 W/mK along with a low coefficient of thermal expansion (CTE) 6 × 10–6/K.

Effect of Thermal Treatment on Coercivity of SmCo<sub>5</sub> Sintered Magnets

Permanent magnet materials composed of transition and rare earth metals exhibit high energy products. Samarium cobalt magnets are developed and research is done to have high coercivity. Chemistry is varied from 34 to 36 weight percent of samarium in Sm1Co5 compound. Effect of chemistry and sintering treatment temperatures on final properties has been studied. Magnets are manufactured by powder metallurgical technique involving isostatic pressing and sintering in inert atmosphere at temperatures range of 1140-1170°C. Then the magnets are subject to post sintering aging treatment in temperature range of 800-900°C. It is observed that coercivity of Sm1Co5 magnet varies with aging temperature and can be improved by post sintering aging treatment.

Friction of PM ferritic stainless steels at temperatures up to 300 °C

Two ferritic stainless steels (409Nb and 434L) manufactured through powder metallurgical techniques were wear tested at different temperature conditions (up to 300 °C). Two sliding speeds were used, and tests were carried out against a wrought austenitic stainless steel. Materials’ wear performance was characterized through friction coefficients and analysis of wear tracks was carried out through scanning electron microscopy. Results have shown an adhesive wear mechanism. Oxidized ferrite particles have also been found on wear tracks.

알칼리 표면개질을 통한 다공성 알루미늄 합금의 하이브리드 기공구조 형성

To improve the filtration efficiency of porous materials used in filters, an extensive specific surface area is required to serve as a site for adsorption of impurities. In this paper, a method for creating a hybridized porous alloy using a powder metallurgical technique to build macropores in an Al-4 wt.% Cu alloy and subsequent surface modification for a microporous surface with a considerably increased specific surface area is suggested. The macropore structure was controlled by granulation, compacting pressure, and sintering; the micropore structure was obtained by a surface modification using a dilute NaOH solution. The specific surface area of surface-modified specimen increased about 10 times compare to as-sintered specimen that comprised of the macropore structure. Also, the surface-modified specimens showed a remarkable increase in micropores larger than 10 nm. Such a hybridized porous structure has potential for application in water and air purification filters, as well as membrane pre-treatment and catalysis.

High-temperature mechanical and electrical properties of W-particle-reinforced Cu-matrix composites from improved electroless plated powders

Copper (Cu)-matrix composites combine the high electrical and thermal conductivities of Cu with the enhanced wear resistance and strength of the reinforcement material, and are therefore widely used for electrical contact applications in a diverse range of fields. In the current study, tungsten-reinforced copper (W—Cu) composite powders are fabricated using a novel electroless Cu plating process in which the homogeneity of the powder mixture is improved via the use of an ultrasonic agitation technique. The volume content of the tungsten particle reinforcement in the composite specimens is 3, 6, and 12 per cent, respectively, and standard powder metallurgical techniques are then applied to produce the final composite powders. The mechanical and electrical properties of the composite powders are evaluated at room temperature and at temperatures ranging from 100 to 300 °C. Fracture surfaces of the composite samples are ana-lysed using scanning electron microscopy. The results show that the mechanical properties of the W—Cu composite samples are significantly better than those of pure Cu specimens, particularly at higher temperatures. Furthermore, the addition of 3 vol% W particles to the W—Cu composite is found to yield a reduction of not more than 2 per cent in the electrical conductivity of the composite sample compared to that of a pure Cu specimen. Overall, the results indicate that the optimal mechanical and electrical properties are obtained by mixing pure Cu powder with 3 vol% of Cu-plated W particles with a mean dimension of 1 μm.

Microstructure and properties of Ti(C,N)–Mo2C–Fe cermets

Abstract Ti(C,N)–15%Mo2C–20 wt%Fe cermets are prepared according to conventional powder metallurgical techniques. The microstructures and properties of the novel cermets are studied. The result shows that Mo2C helps to improve the wettability between Ti(C,N) and Fe, hence cermets with full densification and homogeneous microstructure can be achieved. Typical core–rim structure can be seen in the Ti(C,N)–Fe cermet with Mo2C addition. The cores appear dark and the rims are mainly gray in BSE images, and they are identified to be Ti(C,N) ceramic hard phase and (Ti,Mo)(C,N) solid solution, respectively. Mo2C appears to affect the Ti(C,N) grain size slightly due to the nature of Fe binder. Mechanical properties including hardness and transverse rupture strength are also enhanced due to the addition of Mo2C.

A practical fabrication method for the advanced heterogeneous fuel with magnesia containing minor actinides

Fabrication tests on advanced heterogeneous fuel with MgO were carried out for the purpose of establishing a practical fabrication method. Advanced heterogeneous fuel consists of spheres (diameter greater than 100 μm) of a minor actinide oxide and MgO inert matrix (macro-dispersed type fuel). Macro-dispersed type fuel pellets with a high density above 90% T.D. were successfully fabricated. In addition, the fabricated pellets showed a homogeneous dispersion of near spherical host phase granules. These were attained by optimization of the fabrication process and conditions; i.e. a preliminary heat treatment of raw powders of host phase, an adjustment of pressure at the granulation process, deployment of a spray-dry process for MgO sphere preparation and sintering in a He atmosphere. From these results, a practical fabrication method for MgO-based macro-dispersed type fuel based on a simple powder metallurgical technique was established.

Hybridized porous structure of Al alloy by surface modification of pores

To improve the filtration efficiency of porous materials used in filters, an extensive specific surface area is required to serve as a site for adsorption with impurities. In this paper, a method for creating a hybridized porous alloy using a powder metallurgical technique to build primary pores in an Al-4 wt% Cu alloy and subsequent surface modification for a secondary pore surface with a considerably increased specific surface area is suggested. The specific surface area increased from 0.7 m2/g for the non-treated specimen to 7.3 m2/g for the 0.005 M NaOH-treated specimen. The surface-modified specimens showed a remarkable increase in micropores >10 nm. The primary pore structure was controlled by granulation, compacting pressure, and sintering; the secondary pore structure was obtained by a surface modification using a dilute NaOH solution.

Fabrication of 316-L stainless steel micro parts by softlithography and powder metallurgy

This paper presents an approach to fabricate 316-L stainless steel micro parts with complex shapes using soft lithographical and powder metallurgical techniques. The process includes production of high quality deep micro SU-8 master moulds and their negative replicas in polydimethylsiloxane (PDMS). Then the PDMS soft moulds are filled with slurry containing superfine (< 4 um) stainless steel particles and binder. When the slurry is dry, green patterns are removed from the PDMS moulds before the patterns are de-bound and sintered in the tube furnace at 1200 in forming gas atmosphere. The resultant micro parts show high shape retention. The linear shrinkage of the sintered part is measured and found to be 17%.

A Study on Grinding Performance of Porous NiTi Shape Memory Alloy

The machining performance of porous NiTi shape memory alloys prepared using powder metallurgical production technique has been investigated experimentally in the grinding operation. Grinding force ratio, specific grinding energy, surface characteristics were detected. The result reveals that, much difference of grinding characteristics exists among three kinds of NiTi alloy because of the pore rate and the mechanical performance induced by TiH2. Under the experimental conditions, the integrated effects of predominant plastic flow and slight brittle fracture were taken for porous NiTi alloy during grinding. Additionally, the grinding parameters should be chosen carefully, otherwise the surface quality deteriorates and even the microcrack perhaps appears.

Fabrication of Micro Porous Aluminum by Powder Sintering

Highly porous materials with a cellular structure are known to have many interesting combinations of physical and mechanical properties, such as very low specific weight combined with high thermal conductivity. However, when the pore size of the foam metal grows, the strength maintenance is scarce because the array of the pore is not uniform. In the present work, micro porous aluminum with porosities between 5% and 50% and pore sizes of 20～50 μm was produced by applying the powder metallurgical technique, i.e. by sintering the aluminum metal powders and PMMA powder mixture at 913 K. The effect of sintering temperature on the compressive properties of porous aluminum was investigated. The effects of particle size and fraction of space holding particle and metal powder on the porosity pore size and mechanical properties of porous sintered specimens were mainly investigated. The pore size of porous aluminum can be controlled by changing the PMMA powder diameter. The results show the fabrication of the micro porous aluminum with middle porosity and high strength is possible.