Alloy Sintered Research Articles

Preparation of W-Ni-Cu Alloy Powder by Hydrogen Reduction of Metal Oxides

The effect of powder processing on the microstructure and sinterability of the heavy alloy W-Ni-Cu was investigated. The heavy alloy powders were prepared by the ball milling and hydrogen reduction of metal oxide powders. As the milling time increased, the size of the powder mixture decreased and at 5 h of milling was found to be about 2.5 μm. Microstructural analysis revealed that the powder mixture was changed to W and NiCu alloys with an average particle size of about 200 nm after hydrogen reduction at 800°C for 2 h. The reduction kinetics of the oxide powder mixture was evaluated by the amount of peak shift with heating rates using TGA in a N<sub>2</sub>-10% H<sub>2</sub> atmosphere. The activation energy of the reduction reaction, calculated from the slope of the Kissinger plot, was measured to be 42.8 kJ/mol for CuO, 57.9 kJ/mol for NiO, and 50.1~112.6 for kJ/mol WO<sub>3</sub>. The relative densities of the heavy alloy sintered at 1100oC and 1200oC using oxide powder were 81.4% and 96.0%, while the specimen using metal powder as a raw material showed a relatively low value of 67% and an inhomogeneous microstructure. It was explained that the changes in sintered microstructure with different powder synthesis methods are mainly due to the powder characteristics, such as the size of the particles of the initial mixed powder.

Mechanical Properties of Ti–5Al–5V–5Mo–3Cr Alloy Sintered From Blended Elemental Powders

The field-assisted sintering technique (FAST) was successfully used to sinter, homogenize, and age the Ti–5Al–5V–5Mo–3Cr (Ti-5553) aerospace alloy from blended elemental powders in a single processing run. Sintering at a comparatively high temperature of 1500 °C assured chemical homogeneity of the material. Subsequently, without cooling to the room temperature, the temperature was lowered to 600 °C for 30 min to provide annealing treatment and to produce a desired lamellar α + β microstructure. Using an in-house designed assembly, a fully dense rod of 15 mm in diameter and 70 mm in length was successfully sintered. Microstructural and mechanical properties of the alloy were investigated and compared with the conventionally processed Ti-5553 alloy. A good combination of strength (1183 MPa) and ductility (6 pct) was achieved; these values are fully comparable to the conventional cast, forged, and aged Ti-5553 alloy. It was shown that homogeneous Ti-5553 alloy can be produced by FAST, FAST can instantly provide necessary annealing steps, and the FAST process can be upscaled to produce homogeneous rods.

Microstructure and mechanical properties of Co-containing Ti-48Al alloys prepared from irregular pre-alloyed powder

Poor sinterability of powder metallurgy TiAl-based alloy is an important factor that restricts its industrial production. In this paper, we improve the sinterability of Ti-48Al alloy by adding Co element. In such case, the relative density of Ti–48Al based alloy sintered at 1250 ℃ increases from 82.6% to 96% with an increase of Co content from 0 to 1.5 at%. The densification improvement is caused by liquid TiAl2Co phase, which is formed at 1230 ℃. Then, uniform and fine near-γ microstructure is obtained, and the grain size increases with the increasing of Co content. More than 70% of grains in the Ti-48Al-0.5Co alloy are smaller than 2 µm. Overall, Ti-48Al-0.5Co alloy has better comprehensive performance, with compressive strength of 2533 MPa, yield strength of 683 MPa and fracture strain of 29.5%.

Microstructure and Mechanical Properties of Ni–Cr–Y2O3 Alloy Sintered Powder Composed of Oxide-Embedded Metallic Particles

In this study, oxide (Y2O3)-embedded Ni particles were fabricated via a new process. The process involves the mechanical hydrogenation of Ni–Y alloy into Ni–YH2 and the selective oxidation of Ni–YH2 to Ni–Y2O3. The alloy powders were prepared for sintering by the mechanical alloying of a mixed powder. The powder was prepared with a desired composition (Ni–20wt.%Cr–1.2wt.%Y2O3) by adding Ni and Cr powders to the Ni–Y2O3 composite prepared by the new process. For comparison, a mixed powder with the same composite was prepared using a conventional mechanical alloying (MA) approach. Samples of the two powders were sintered by SPS at 850, 900, 950, and 1,000 <sup>o</sup>C. The relative densities of all samples were higher than 99.7% at all sintering temperatures. The oxide particles and matrix grain sizes of the Ni–20Cr–1.2Y2O3 alloy prepared by this new process were finer than those in alloys fabricated by conventional MA processes. Therefore, the improvement in the mechanical properties of the Ni–20Cr–1.2Y2O3 alloy prepared by the new process was attributed to the refinement of the oxide particles.

Microwave sintering of tungsten heavy alloys

To understand microwave sintering of heavy alloys with high tungsten content, 93W-4.9Ni-2.1Fe alloy was sintered using a 6 kW, 2.45 GHz microwave sintering furnace at 1783 K (1510˚ºC) and 1793 K (1520˚ºC). The alloy sintered at 1793 K (1520˚ºC) achieved full densification and had improved microstructural features, superior mechanical properties compared to 99.4% densification and relatively inferior properties obtained in the alloy sintered at 1783 K (1510˚ºC). This study also includes a comparison between microwave sintered and conventionally sintered 93W-4.9Ni-2.1Fe alloy (sintered at 1793K (1520ºC)). Contrary to the full densification and superior mechanical properties obtained in microwave sintering, conventional sintering at 1793K (1520ºC) resulted in only 99.6% densification and substantially inferior properties. Analyses of microstructure and fracture surface revealed that key microstructural parameters such as tungsten grain size, tungsten-tungsten contiguity, matrix volume fraction and also the fracture mode were significantly different between the alloys processed by the two routes. Possible reasons behind dissimilar densification, significantly different microstructures and mechanical properties obtained between these two modes of sintering, are also discussed in this study.

Effect of Powder Particle Size of Tin Based Alloy Sintered via Hybrid Microwave and Conventional Furnace

Microwave processing of metal alloy powders have gained considerable potential in the field of material synthesis. This paper aims to present the effect of powder particle size of Tin Based Alloy sintered using different type of heat source. Tin (Sn) based alloy containing two different sizes, 10 μm and 150 μm of Sn powder were successfully sintered using hybrid microwave and conventional sintering. The overall processing time was reduced by about 93% through microwave sintering. The comparative analysis is based on densification parameter, microhardness, microstructures and XRD detected phases of the specimens. All specimen with 10 μm sintered in microwave exhibited 90% of theoretical density while exhibited 86% lower porosity and possessed 30% higher in microhardness value.

Spark Plasma Sintering of Fe-Cr-Mo-P-B-C-Si Amorphous Alloy

In the present work, synthesis of bulk Fe amorphous alloy by mechanical alloying of 70Fe-15Cr-4Mo-5P-4B-1C-1Si powders followed by consolidation of powders using Spark Plasma Sintering process is reported. The evolution of phase, microstructure, relative density and hardness of amorphous alloy as a function of spark plasma sintering temperature is discussed. Transmission electron microscopy investigation has shown partial divitrification of amorphous matrix into nanocrystalline phase during spark plasma sintering of amorphous Fe alloy. The hardness of amorphous alloy sintered at 525 – 575°C are in the range of 675 - 725 MPa.

Mechanical Properties of Zr Added CoCrMo Alloy Sintered Compact Produced by MIM Proces

The main objective of the present work is to evaluate the effects of the addition of zirconium on the mechanical properties of Co-29Cr-6Mo sintered parts produced by metal injection molding process using water atomized powder as raw materials. The results are summarized as follows;1) The sintering density of Co-29Cr-6Mo alloy powder was increased by the addition of zirconium in both sintering atmosphere of argon and nitrogen.2) Mechanical properties were also improved by the addition of zirconium in both sintering atmosphere of argon and nitrogen. By using MIM process, the products having better mechanical properties compared with casting method were obtained.3) HIP treatment of sintering products increased the relative density by about 4 % caused by diminishing pores. This densification produced the increase of tensile strength and 0.2 % proof stress by about 100 MPa.

Sintering of Fe-Ti alloy in the ammonia plasma of a glow discharge

The phase composition, structure, and properties of iron-titanium antifriction alloy sintered in the ammonia plasma of a glow discharge are studied. The effect of parameters of the sintering process on the structure and properties of the alloy is determined.

Sintering and mechanical properties of iron alloy sintered with liquid iron-boron phase: M. Courbiere, L. Akermann (Pechiney, France)

Sintering and mechanical properties of iron alloy sintered with liquid iron-boron phase: M. Courbiere, L. Akermann (Pechiney, France)

Tungsten Base Alloys with Low Thermal Expansion Coefficient. (1 st Report)

The physical and mechanical properties of W-Ni alloys of 0.1-2.0% Ni prepared by the nickel activated sintering were studied to obtain an alloy having electrical conductivity and thermal expansion coefficient nearly close to that of pure tungsten. Several interesting results were obtained as follows.(1) The sintering of these alloys appreciably proceeds at temperature ranging from 1000°C to 1300°C.The density of alloys sintered at 1200°C is 18.5 to 18.8g/cm3 (density ratio 97% up).(2) Value of electrical conductivity of an alloy sintered at about 1200°C (about IACS 28%) is maximum and it decreases as sintering temperature increases.(3) The W-Ni alloy containing 2% Ni sintered at 1000°C has the higher hardness (Hv 550) than the swaged tungsten.These results were obtained by the measurements of magnetic properties and microhard-ness, and the X-ray diffraction method.