Materials Science Forum Vols. 534-536

Abstract: To study of the sintering behaviour of the Fe-0.8Mn-0.5C powder system the cylindrical specimens with a density of ~7.0 g/cc were sintered in container at the temperature of 11200C for 30 min in a gas mixture of 7%H2/93%N2 with the inlet dew point of -600C. The composition (CO/CO2- content) and the dew point of the flowing and “container micro-climate” atmospheres during the whole sintering cycle were monitored. It was shown, that carbothermical reduction and formation esp. CO/CO2 occurs in two different temperature ranges. Three peaks of dew point profile also can be distinguished during sintering cycle. Following sintering the changes of ferromanganese particles, Mn-content distribution and microstructures around the Mn-source were micro-analytical evaluated at cross-section of specimens using the SEM with EDX microanalyses. The results showed that manganese travels through porous iron matrix up to ~60 μm. The type of local microstructure constituents is determined by the local Mn- and C contents.

Abstract: Al-8Fe-2Mo-2V-1Zr alloy powders were prepared by gas atomization and melt spinning method. In melt spinning technique, melt spun ribbons were pulverized by a speed rotor mill to make a powder shape. In order to produce a bulk form, powders were canned and hot extruded in the extrusion ratio of 25 to 1 at 693K. For the gas atomization and hot extrusion processed bulk material, equiaxed grains with the average size of 400 nm and finely distributed dispersoids with their particle sizes ranging from 50nm to 200nm were observed to display a characteristic nano-structured feature over the entire region. For the melt spun and hot extrusion processed alloy, a refined microstructural feature consisting of equiaxed grains with the average size of 200 nm and fine dispersoids with their particle sizes under 50 nm appeared to exhibit a difference in microstructure. Yield strength of the latter alloy was higher than that for the former alloy up to elevated temperatures. The maximum yield strength was measured to about 800 MPa at room temperature for the latter alloy.

Abstract: A new approach is explored to achieve sintered aluminium alloy from metallic powder mixtures without compression or adding Mg. In this approach, mixtures of micron-sized aluminium powder (average size of 2.5 μm) and nano-sized alloying elemental powder of Cu and Sn (less than of 70nm), at appropriate proportions to compositions of Al-6wt%Cu, Al-6wt%Cu-3wt%Sn with and without adhesive binder were prepared by magnetic stirring. Then, the powder mixture was poured into a crucible and heat treated at a temperature of 600°C for 11 hours in inert atmosphere of N2 or Ar. In this paper, we investigate the debinding behavior of loosely packed Al-based powder mixture and the microstructural development and mechanical property sintered parts using a combination of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffractrometry (XRD) and hardness test.

Abstract: P/M aluminium components are attracting interest in an increasing variety of industries due to the possibilities for weight saving in engineering parts. There are many processes for manufacturing from powder feedstocks that are either in production, becoming commercialised or still undergoing development. The nature of these processes and the required properties of the end products mean that powders of different particle size, shape, composition and microstructure must be produced. The requirements of various processes requiring aluminium and aluminium alloy powders for metal matrix composites, laser sintering, powder forging and metal injection moulding are discussed in relation to powder particle size and structure. The key requirement of the powder manufacturer is to supply cost effective materials for these different processes. This may require compromises to be made by the supplier and consumer while the techniques evolve from development to large scale production.

Abstract: Titanium alloys and Titanium alloy-based particulate composites were synthesized using the blended elemental P/M route. First, processing conditions such as the fabrication of master alloy powder were investigated. Ti-6Al-4V, Ti-5Al-2.5Fe, Ti-6Al-2Sn-4Zr-2Mo, IMI685, IMI829, Timetal 1100 and Timetal 62S, and Ti-6Al-2Sn-4Zr-2Mo/10%TiB and Timetal 62S/10%TiB were then synthesized using the optimal processing conditions obtained. The microstructures and mechanical properties such as tensile strength and high cycle fatigue strength were evaluated.

Abstract: We successfully developed Al -Si -Transition Metal (TM) -Rare Earth (RE) Powder Metallurgy (P/M) alloy with fine microstructure, which has high strength at high temperature. For example, at 473K, the ultimate tensile strength was 290MPa and fatigue strength on 107 cycles was 130MPa, which is an 80% improvement compared with conventional Aluminum cast alloys. This material was compacted rapidly solidified powder and directly consolidated by hot extruding or forging. The microstructure consists of fine Al crystal grains (grain size; around 200-500nm), and inter-metallic compounds. Before consolidating, rapid heating was performed on powder compaction in order to keep the fine microstructure in powder state. The effect of plastic deformation on consolidating was examined to stabilize properties of this material. The mechanical properties of the present alloy are expected] to contribute to improve performance of various automobile engine parts.

Abstract: Study about the feasibility and effect of high-energy ball milling on a specific Mg alloy under protection medium of alcohol was presented via comparing with conventional vacuum milling. More fine particles with wider powder size distribution but more irregular shape were shown from image analysis of the SEM pictures of the powder milled under alcohol. No obvious oxide was revealed from the X-ray diffraction of the two kinds of Mg alloy powders with limited milling time. And since slip induced in a preferential direction, the (002) texture was formed in the Mg alloy powders at the initial stage of alcohol milling. With deformation occurred randomly, the texture disappeared regularly. More O and Fe contaminants were introduced into the powders milled under alcohol according to the EDS analysis, for which the hot-pressed Mg alloy samples fabricated with that powders exhibited lower UTS.

Abstract: Friction stir welding technique (FSW) has many advantages in terms of tool design, rotational speed and traveling speed, and can be adjusted in a precise manner. It enables heat input into the system to be controlled. In this study, Aluminum powders were compacted at 350,400 and 450 MPa pressure and sintered at 450 oC temperature for 30 minutes in Ar atmosphere. Sintered powder metal parts were joined to each other by FSW at the speed of 1800 rpm and traveling welding speed 200 mm/min under a constant friction force. The results show that the amount of porosity affects the weldability of powder metallurgy (P/M) parts. Furthermore, the porosity and microstructural evolution of the Aluminum also affected the hardness values of the tested materials.

Abstract: MgZn4.3Y0.7 alloy powders were prepared using an industrial scale gas atomizer, followed by warm extrusion. The powders were almost spherical in shape. The microstructure of powders as atomized and bars as extruded was examined as a function of initial powder size distribution using Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscope (EDS) and X-ray Diffractometer (XRD). The grain sizes were decreased with extruding as well as decreasing the initial powder sizes. Both the ultimate strength and elongation were enhanced as the initial powder sizes were decreased.