Densification,microstructure, and properties of W-Mo-Cu alloys prepared with nano-sized Cu powders via large electric current sintering

This study rapidly fabricated a novel W-Mo-Cu alloy by large current electric field sintering at a relatively low temperature, and the effects of the powder size of Cu on the densification, microstructure, and properties were comprehensively investigated. The particle size of Cu did not influence the phase type but significantly affected the densification, microstructure, and properties. XRD and TEM results showed that the alloy contained three new phases aside from W, Mo, and Cu phases, i.e., Mo-W ordered phase, Mo-Cu solid solution, and Cu_0.4W_0.6 intermetallic compound. Copper powders with smaller sizes were beneficial to improving the distributional homogeneity of elements and the sintering densification. Therefore, the alloy prepared with 100 nm Cu powders had a denser and more homogeneous microstructure and better comprehensive properties than that prepared with 5 μm Cu powders. Overall, the W-Mo-Cu alloy prepared with 100 nm Cu powders at 980 °C proposed the best comprehensive properties, and its relative density can reach 98% approximately.     

Effects of Mg content on aging behavior of Al4CuXMg PM alloy

Starting with elemental (pre-mixed) powders for producing shaped powder metallurgy alloys provides some advantages over a pre-alloyed system. The premixed powders are softer than prealloyed powders and therefore by using premixed powders it is possible to have higher compact densities and within a longer die life. In this research work, elemental aluminum powder was mixed with copper and magnesium in various ratios. They were compacted, sintered and heat treated in order to produce light but strong Al-based powder metallurgy alloys. The main focus of this paper is on the effects of micro to macro scale addition of magnesium on the aging response of Al4Cu alloys. Four per cent Cu gives Al powder metallurgy alloy a good control of sintering and a large space for solution treatment. Minor addition of Mg with little amount of Fe, comes from the based Al and Cu powders, enhances the hardness values of Al4Cu powder metallurgy alloys. Highest hardness value was 118 HB obtained from 24 h aged Al4Cu2Mg alloy.     

Sintering of elemental carbonyl iron and carbonyl nickel powder mixtures

Iron-nickel alloys with compositions ranging from pure iron to pure nickel at increments of 10 wt% have been prepared by mixing fine elemental carbonyl iron and nickel powders, and sintering at temperatures between 1200–1350°C. The addition of nickel to iron promoted densification and avoided abnormal grain growth at low concentrations. However the densification was retarded when the iron and nickel had approximately equivalent concentrations. As the concentration of nickel increased, the room temperature structures of the alloys gradually changed from α-Fe into γ-(Fe, Ni), with Fe-30 wt% Ni and Fe-40 wt%, Ni containing both phases. The relative abundance of each phase was determined by the degree of compositional homogeneity achieved in sintering. This revised version was published online in November 2006 with corrections to the Cover Date.     

Experimental study on the plastic deformation and densification characteristics of some sintered and heat treated low alloy powder metallurgy steels

Sintered low alloy steels containing the alloying elements molybdenum, copper and titanium were synthesised through powder metallurgy route from mixed elemental powders to yield the compositions: Fe–0.5% C, Fe–0.5% C–2% Cu, Fe–0.5% C–2% Mo and Fe–0.5% C–2% Cu–2% Mo–2% Ti. Green cylindrical compacts were made using a 1000 kN hydraulic press using suitable cylindrical die-punch combination. The ceramic coated cylindrical preforms were sintered at 1000 ± 10 °C in a muffle furnace for a period of 120 min. After sintering, the preforms were subjected to different heat treatment processes, namely, heating to 900 °C, soaking for 60 min and quenching in air or oil or cooled inside the furnace. The heat treated preforms were subject to axial upsetting deformations, at various applied loads and their densification behaviours were compared. The influence of various heat treatment processes on deformation and densification of the alloys was studied and correlated with their microstructures. The plain carbon steel preforms were observed to respond well to the three heat treatment cycles by way of exhibiting the highest levels of densification and plastic deformation. However, both alloy addition and heat treatment have led to a reduction in densification and deformation of the alloy steel preforms. Presence of titanium carbide particulates in the microstructure of the Ti-alloyed steel has played a significant role in reducing the densification as well as deformation. The basic ferritic–pearlitic microstructure of Fe–0.5% C steel has essentially promoted the largest deformation levels coupled with higher densification.     

Comparison of densification and distortion behaviors of W-Ni-Cu and W-Ni-Fe heavy alloys in liquid-phase sintering

This paper aims to correlate the densification and distortion behaviors of liquid-phase sintered 80W-14Ni-6Cu and 80W-14Ni-6Fe heavy alloys with the melting characteristics of the Ni-Cu and Ni-Fe matrices. Differential thermal analysis (DTA) of die-pressed compacts reveals that the melting range of the Ni-Cu matrix is extended from 1235°C to 1453°C by the in situ alloying between elemental Cu and Ni powders, whereas the melting of the Ni-Fe matrix is limited to a narrow temperature range between 1464°C and 1480°C. Dilatometry and furnace sintering tests show that densification due to liquid-phase sintering of 80W-14Ni-6Cu starts at 1287°C and proceeds at a low rate to 1450°C, where full densification without distortion is achieved. In contrast, densification due to liquid-phase sintering of 80W-14Ni-6Fe occurs at a very high rate above 1475°C, and full density can be obtained at 1500°C. For both alloy compacts, distortion is induced by prolonging the sintering time or elevating the sintering temperature after full densification. Crack-like voids develop in the 80W-14Ni-6Cu compact to accommodate the gravity-induced distortion, while spherical pores are dominantly formed in the 80W-14Ni-6Fe compact as a result of water vapor entrapment.     

Effect of Amount of Carbonyl Iron Powders on the Sintering Microstructure, and Mechanical Properties of Fe-4 Cu Alloy Synthesized Using Metal Injection Molding

An atomized iron powder used in conventional powder metallurgy, mixed with 4 wt.% Cu powders was injection molded with carbonyl iron powder and a sintering aid. The use of atomized iron powder can reduce cost, but decreases packing density and sintering rate. To improve the densification of atomized powders, 20-40 wt.% carbonyl iron powder was added for increasing packing density and promoting sintering. The sintered alloy was characterized by the bulk density, mechanical properties, and scanning electron microscope observations. The results of sintering for the samples added with 30 wt.% carbonyl powder show that the relative bulk density, hardness, tensile strength and elongation are up to 83.87%. HRF 92.2, 315.5 MPa and 4%, respectively. The proportion of carbonyl iron powders and sintering temperature were found to influence the relative bulk density and the mechanical properties of the specimens significantly.     

Grinding behavior of WO3, NiO,Fe2O3 by ultrasonic milling parameters control and preparation of nanocomposite powder

Tungsten-based alloys have been widely applied in various industries due to their excellent mechanical properties. Tungsten-based alloys have a high sintering temperature due to the high melting point of tungsten, so the coarse particles negatively affect the mechanical properties of the alloy. This problem can be solved by increasing the densification by reducing the sintering temperature and time by adding nanoparticles with high surface energy. Herein, we fabricated nanoparticle-sized metal oxides by ultrasonic milling to minimize the influx of impurities to improve the densification of tungsten alloys. The main parameters of the ultrasonic milling experiments were ball density and ball layer. Metal oxides prepared by ultrasonic milling showed an average particle size distribution of less than 200 nm, and metal composite powders prepared through subsequent hydrogen reduction also showed nanoparticle size distributions. We believe that this approach will enable the production of improved sintered tungsten-based alloys.     

Effect of powder processing and alloying additions (Al/ZrB2) on the microstructure,mechanical and electrical properties of Cu

The present work elucidates the effect of powder processing conditions (milling/mixing) and conductive alloying element (Al: aluminium) and ceramic (ZrB₂: zirconium diboride) reinforcement addition on the densification, microstructure and electrical conductivity of copper (Cu) processed via hot pressing route. Disregard of alloying element/reinforcement/content or powders preparation method, the density of Cu materials varied between 92.16 and 99.76% ρ_th (theoretical density) after hot pressing at a low temperature of 500 °C. In case of Cu-Al alloys, the powder processing method significantly influenced its microstructure and conductivity. Particularly the Cu-Al alloys processed using mixed powders consisted of various phases Cu, α-Cu, γ₁ (Cu₉Al₄), δ (Cu₃Al₂), ζ₁ (Cu₄Al₃), η₂ (CuAl) and θ (CuAl₂) and the Cu alloys prepared using milled powders composed of either only α-Cu or α-Cu and γ₁ (Cu₉Al₄) phases (depending on the Al content). Whereas, only Cu and ZrB₂ phases were observed with the Cu-ZrB₂ composites processed using either milled or mixed powers. In case of Cu-Al alloys, the hardness (0.88–3.41 GPa) and strength (540.30–1120.18 MPa) of Cu increased with the addition of Al. Interestingly, the hardness (0.88–2.55 GPa) and strength (508.50–970.60 MPa) of Cu increased upto 5 wt% ZrB₂ and then they lowered with further addition of ZrB₂. In particular, the hardness and strength of Cu-ZrB₂ composites are lower than Cu-Al alloys reflecting the effectiveness of solid solution strengthening in the Cu alloys as compared to dispersion strengthening mechanism in Cu composite. The pure Cu prepared using milled powders exhibited low conductivity (75.70% IACS) than Cu processed using as-received/un-milled powders (97.00% IACS). Also, the Cu-ZrB₂ composites measured with better electrical conductivity than Cu-Al alloys. Depending on the milling conditions and alloying/reinforcement amount, the conductivity of Cu-ZrB₂ composites varied between 44.10 and 88.70% IACS.     

Effect of carbon on the density,microstructure and hardness of alloys formed by mechanical alloying

This work aimed to produce iron-based alloys containing resistant microstructures to improve the mechanical properties of the resulting alloy. The effects of both carbon content and compaction pressure on the microstructure, density and hardness of the alloys were examined. Iron-based alloys with initial carbon contents of 0.5%, 1%, 2% and 3% were produced by powder metallurgy following a process that involved ball milling elemental powders, cold pressing and sintering. The composition, density, microstructure, porosity, hardness and ductility of the alloys depended on both compaction pressure and carbon content. As the carbon content increased, the amount of the resistant microstructure bainite in the alloys also increased, as did their hardness. In contrast, the density and ductility of the alloys decreased with increasing carbon content. This study shows that formation of the resistant microstructure bainite in alloys fabricated by powder metallurgy is influenced by both the initial carbon content of the alloy and compaction pressure during cold pressing.     

Copper Alloys From Metal Oxide Precursors for High Conductivity Applications

Extrusion of oxide powders allows fabrication of thin-walled metal articles to produce controlled-geometry, low-density copper alloy architectures. Shapes formed with copper oxide powders mixed with alloying oxides are reduced and sintered to produce high relative densities in the thin walls. This technology has produced square-cell honeycomb extrusions, which are being characterized for heat sink applications. This effort is to determine the bulk properties of alloys produced by this type of thermo-chemical powder processing and to explain behavior based on the final chemistry and microstructure of the alloys. Compositions investigated include Cu, Cu-Ni, Cu-Ag, W-Cu, Cu-Invar, Cu-Al₂O₃, and Cu-Cr alloys. Alloys have been characterized for relative density, thermal conductivity, and grain size. Mechanical properties including tensile and yield strength and elongation were measured on Cu-Ni and Cu-Ag, and the results were analyzed based on porosity and composition of the alloys. Properties were compared to alloys made through conventional processing and powder metallurgy.     

Preparation of Fe3AI based iron aluminides from elemental and prealloyed povvders

Abstract

Iron aluminides were prepared by a powder metallurgy process from elemental powders, mixtures of prealloyed and elemental powders, and prealloyed powder. The sintering behaviour of various powders was studied using scanning electron microscopy, optical microscopy, and density measurement. It was found that sintering of elemental powder involved two distinct processes, i.e. alloying and densification, but sintering of prealloyed powder involved densification alone. The addition of prealloyed powder to elemental powders was helpful in restraining the swelling of sintered samples, the degree of swelling of sintered samples being reduced as the amount of prealloyed powder increased. For samples made from Fe-25 at.-%Al prealloyed powder, remarkable shrinkage was measured after sintering at 1250°C for 1 h. Within the correct range, their density increased with sintering temperature and time, but prolonged sintering at high temperature resulted in the loss of aluminium and a two phase microstructure. The difference in sintering behaviour between the various powders was discussed on the basis of thermodynamics.     

Microstructural studies on nanocrystalline oxide dispersion strengthened austenitic (Fe–18Cr–8Ni–2W–0.25Y<Subscript>2</Subscript>O<Subscript>3</Subscript>) alloy synthesized by high energy ball milling and vacuum hot pressing

In the present work, nanostructured (Fe–18Cr–8Ni–2W) austenitic base and oxide dispersion strengthened (ODS) alloy powders were produced through mechanical alloying and these nano powders were consolidated by vacuum hot pressing. The results showed that initially bcc solid solution formed in both the alloys and this transformed to fcc with continued milling. The bcc solid solution formation and the subsequent transformation to fcc were significantly faster in the ODS alloys when compared to the base alloy. In the ODS alloy, a grain size of ~25 nm is achieved within 5 h of milling. Study of variation of microhardness of mechanically alloyed powder particles with grain size showed linear Hall–Petch kind of behavior. Following vacuum hot pressing of mechanically alloyed powders, nearly fully dense (>99% of theoretical density) compacts were obtained with a grain size of ~80 nm. The bulk hardness of base and ODS alloys are ~530 and ~900 HV, respectively. These are significantly higher than the values reported in the literature so far. The enhanced strength the ODS alloy is due to increased dislocation density and presence of fine dispersoids along with the nanocrystalline grains.     

Production of new titanium alloy for orthopedic implants

The beta titanium alloys is one of the most promising groups of the titanium alloys. This fact is due to the good formability, mechanical properties and potential applications; moreover, these alloys present the highest level of mechanical, fatigue and corrosion resistance. The beta titanium alloys present the lowest elastic modulus, an interesting property for orthopedic implants. A β alloy recently developed for this application is Ti–35Nb–7Zr–5Ta. In this work, the alloy was produced by powder metallurgy, unique available alternative for obtaining parts with porous structure (until 50% of porosity), that is one important characteristic for the osteointegration. The Ti–35Nb–7Zr–5Ta samples were manufactured by blended elemental method from a sequence of uniaxial and cold isostatic pressing with subsequent densification by sintering among 900 at 1700 °C, in vacuum. The objective of this work is the analysis of alloy microstructural evolution from the elemental powders dissolution under the increase of the sintering temperature. The alloy was characterized by scanning electron microscopy, X-ray diffraction and Vickers microhardness measurements. Density was measured by Archimedes method. The results show that a β-homogeneous microstructure is obtained in the whole sample with the increase of sintering temperature. With the beginning of the β-stabilizers (Nb and Ta) dissolution, at low sintering temperatures, there is the formation of an intermediary Widmanstätten (α+β) phase.     

Effect of Re on microstructural evolution and densification kinetics during spark plasma sintering of nanocrystalline W

In the present investigation, nanocrystalline W and W-xRe (x = 3, 5 wt.%) alloy powders were produced by mechanical milling/alloying using high energy ball milling. The nanocrystalline nature (∼50 nm) of these powders was validated by the Rietveld refinement of their respective X-Ray diffraction patterns. Subsequently, spark plasma sintering of the ball milled powders was carried out. It was observed that pure W was not able to densify completely (relative density of 93%) at a temperature of 1500 °C. However, the addition of 5 wt.% Re resulted in near complete densification (relative density of 97%) at the same sintering temperature. The enhanced densification of W-Re powders is mainly attributed to the ductilising effect of Re assisted by the nanocrystallinity of powders, and the application of pressure during sintering.     

Influence of additions of Zr, Ti–B, Sr, and Si as well as of mold temperature on the hot-tearing susceptibility of an experimental Al–2% Cu–1%?Si alloy

This study was undertaken to investigate the effects of chemical composition and mold temperature (MT) on the hot-tearing susceptibility (HTS) of an experimental Al–2% Cu–1% Si alloy using a constrained rod casting mold. The HTS results were then compared with 206 (Al–5 wt% Cu) alloys containing the same additions. In general, the Al–2% Cu–1% Si based alloys exhibited higher resistance to hot-tearing than did the 206-based alloys. It was found that an elevated MT is beneficial in reducing the HTS of the Al–2% Cu–1% Si and 206 alloys in that the HTS value decreased from over 21 to less than 5, as the MT was increased from 250 to 450 °C. Increasing the Si content reduced the HTS of the Al–2% Cu–1% Si alloy considerably; this reduction may be attributed to an increase in the volume fraction of eutectic in the structure. The addition of Sr caused deterioration in the hot-tearing resistance of the base alloy due to the formation of Sr-oxides and an extension of the freezing range of the alloy. The refinement of the grain structure obtained with the Zr–Ti–B addition decreased the severity of hot-tearing as a result of an increase in the number of intergranular liquid films per unit volume and a delay in reaching the coherency point. It was also observed that α-Fe intermetallic particles may impede the propagation of hot-tearing cracks. The Al–2% Cu–1% Si alloy with 1 wt% Si addition was judged to be the best composition in view of its low HTS.     

Investigation on preparation and mechanical properties of W–Cu–Zn alloy with low W–W contiguity and high ductility

In order to improve the mechanical properties of the W–Cu alloy, the W–Cu–Zn alloys with low W–W contiguity were fabricated by three different preparation methods. For the first method, the mixed powder of copper-coated tungsten powder and Zn powder was sintered by SPS (Spark Plasma Sintering) process. For the second method, the mixed powder was processed by CIP (Cold Isostatic Pressing) before SPS. For the third method, a skeleton of the copper-coated tungsten powder was prepared by CIP, and then the skeleton was infiltrated with H70 brass. The microstructure, mechanical properties and failure mechanism of the prepared W–Cu–Zn alloys were investigated. The results show that the W–Cu–Zn alloy fabricated by the third method achieves a high relative density of 98.4% and a low W–W contiguity of 10%. The alloy exhibits a high dynamic compressive strength of 1000 MPa, with a high critical failure strain of 0.7. The Cu-Zn matrix of the alloy fabricated by the third method is composed of α-phase Cu–Zn alloy and Cu₃Zn particles. The homogeneous distribution of Zn in the matrix manifests good solution strengthening effect and the uniformly distributed Cu₃Zn particles has a strong precipitation strengthening effect, which are both responsible for the evidently enhanced mechanical properties.     

Magnetic properties of iron-base b.c.c. alloys produced by mechanical alloying

The structure and magnetic properties of Fe-M (M = Zr, Hf, Co or Si) alloy powders produced by mechanical alloying (MA) of elemental powders or a mixture of elemental powders and alloy powders have been examined. The MA Fe-Zr and Fe-Hf powders have a non-equilibrium b.c.c. phase in the composition range above 90 at% Fe. The coercivity of the MA Fe-Zr and Fe-Hf powders exhibits a minimum value (1300 A m⁻¹) combined with a high magnetization of 2.2×10⁻⁴ Wb m kg⁻¹ at 95 at % Fe, which corresponds to the concentration of zero magnetostriction. Although the compacts made from the MA b.c.c. Fe-Zr powders do not exhibit good soft magnetic properties, the permeability of the compacts made from the MA Fe-Co powders annealed at 1173 K for 18 ks in H₂ is nearly the same as that of the alloy ingot produced by conventional casting followed by the same annealing treatment. On leave from ALPS Electric Co. Ltd, Nagaoka 940, Japan.     

Formation and crystallization behavior of Fe-based amorphous precursors with pre-existingα-Fe nanoparticles-Structure and magnetic properties of high-Cu-content Fe-Si-B-Cu-Nb nanocrystalline alloys

Structure,crystallization behavior,and magnetic properties of as-quenched and annealed Fe_81.3Si₄O₁₃Cu_1.7(Cu1.7)alloy ribbons and effects of Nb alloying have been studied.Three-dimensional atom probe and transmission electron microscopy analyses reveal that high-number-density Cu-clusters and Pre-existing Nano-sized a-Fe Particles(PN-a-Fe)are coexistence in the melt-spun Cu1.7 amorphous matrix,and the PN-α-Fe form by manners of one-direction adjoining and enveloping the Cu-clusters.Two-step crystallization behavior associated with growth of the PN-a-Fe and subsequent nucleation and growth of newly-formedα-Fe is found in the primary crystallization stage of the Cu1.7 alloy.The number densities of the Cu-clusters and PN-a-Fe in melt-spun Fe8_1.3-xSi₄B₁₃Cu_1.7Nb_xalloys are gradually reduced with enriching of Nb,and a fully amorphous structure forms at 4 at.%Nb,although smaller Cu-clusters still exist.After annealing,2 at.%Nb coarsens the average size(D_α-Fe)of theα-Fe grains from 14.0 nm of the Nb-free alloy to 21.6 nm,and 4 at.%Nb refines the D_α-Feto 8.9 nm.The mechanisms of theα-Fe nucleation and growth during quenching and annealing for the alloys with large quantities of PN-α-Fe as well as after Nb alloying have been discussed,and an annealing-induced oc-Fe growth mechanism in term of the barrier co-contributed by competitive growth among the PN-a-Fe and diffusion-suppression effect of Nb atoms has been proposed.A coercivity(HC)αDα-Fe³correlation has been found for the nanocrystalline alloys,and the permeability is inverse with the H_C.     

Fe基非晶/纳米晶粉末的放电等离子烧结及磁性能

研究了SPS温度对球磨熔体快淬Fe₇₀Cr₈Mo₂Si₅B₁₅粉末以及MA Fe_73.5Cu₁Nb₃Si_{13 5}B₉ 和Fe₈₀C_o4Nb₇B₉纳米晶粉末的烧结块体合金组织结构与磁性能的影响.结果表明: (1)在30MPa/5min条件下,块体合金相对密度随着烧结温度的升高而增加,当烧结温度为1000℃时,Fe₇₀Cr₈Mo₂Si₅B₁5合金相对密度已达99%以上,当烧结温度进一步升高至1050℃后, Fe_73.5Cu1Nb₃Si1_3.5B₉和Fe₈₀Co₄Nb₇B₉合金相对密度也达到99%;(2)烧结块体合金的主要组成相为α-Fe相,尚存在少量的第二相金属间化合物,这些块体合金α—Fe相的晶粒尺寸均处于纳米级范围内,以Fe₇₀Cr₈Mo₂Si₅B₁₅块体合金的晶粒尺寸为最小,其平均晶粒尺寸约50nm; (3)随着烧结温度的升高,这些块体合金的饱和磁感应强度B_s增大,矫顽力H_c随之降低,以Fe₇₀Cr₈Mo₂Si₅B₁₅块体合金的矫顽力H_c(4.1kA·m^-1)最低.     

Effect of carbon on mechanical properties of powder-processed Fe-0.35%P alloys

The present paper records the results of mechanical tests on iron-phosphorus powder alloys which were made using a hot powder forging technique. In this process mild steel encapsulated powders were hot forged into slabs, hot rolled and annealed to relieve the residual stresses. These alloys were characterized in terms of microstructure, porosity content/densification, hardness and tensile properties. Densification as high as 98.9% of theoretical density, has been realized. Microstructures of these alloys consist of single-phase ferrite only. Alloys containing 0.35 wt% P, such as Fe-0.35P-2Cu-2Ni-1Si-0.5Mo and Fe-0.35P-2Cu-2Ni-1Si-0.5Mo-0.15C show very high strength. It was observed in this present investigation that, the alloying additions, such as Si, Mo, Ni, and C to Fe-P based alloys caused increase in strength along with reduction in ductility. Cu reduces porosity of Fe-P alloys. Alloys developed in the present investigation were capable of hot working to very thin gauge of sheets and wires.