Powder metallurgy

About: Powder metallurgy is a research topic. Over the lifetime, 19751 publications have been published within this topic receiving 238540 citations.

Design, Processing, Microstructure, Properties, and Applications of Advanced Intermetallic TiAl Alloys†

Abstract: After almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high-temperature materials are their low density and their good strength and creep properties up to 750 °C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e., concurrent increase of ductility at room temperature and creep strength at elevated temperature. This review gives a general survey of engineering γ-TiAl based alloys, but concentrates on β-solidifying γ-TiAl based alloys which show excellent hot-workability and balanced mechanical properties when subjected to adapted heat treatments. The content of this paper comprises alloy design strategies, progress in processing, evolution of microstructure, mechanical properties as well as application-oriented aspects, but also shows how sophisticated ex situ and in situ methods can be employed to establish phase diagrams and to investigate the evolution of the micro- and nanostructure during hot-working and subsequent heat treatments.

Full sintering of powdered-metal bodies in a microwave field

Abstract: The use of microwaves to process absorbing materials was studied intensively in the 1970s and 1980s, and has now been applied to a wide variety of materials1,2,3,4. Initially, success in microwave heating and sintering was confined mainly to oxide and some non-oxide ceramics5,6,7,8,9,10,11; but recently the technique has been extended to carbide semimetals12,13,14 used in cutting tools. Here we describe the microwave sintering of powdered metals to full density. We are able to sinter a wide range of standard powdered metals from commercial sources using a 2.45-GHz microwave field, yielding dense products with better mechanical properties than those obtained by conventional heating. These findings are surprising in view of the reflectivity of bulk metals at microwave frequencies. The ability to sinter metals with microwaves should assist in the preparation of high-performance metal parts needed in many industries, for example, in the automotive industry.

Formation of amorphous alloys by the mechanical alloying of crystalline powders of pure metals and powders of intermetallics

Abstract: Amorphous powders of Ni32Ti68 and of Ni45Nb55 were synthesized by mechanical alloying (MA) starting from either a mixture of pure metal powders (in the appropriate molar ratio) or from powders of the crystalline intermetallics NiTi2 and Ni45Nb55, respectively. For both alloys, the peak temperature increase (above the average processing temperature) in the powder particles trapped between colliding balls is estimated at 38 K. Thus, the amorphization is attributed to a process other than the formation of local melts followed by the rapid solidification of these melts into the amorphous phase. The amorphization by MA starting from a mixture of pure crystalline powders is attributed to a solid state interdiffusion reaction, the kinetics of which is controlled by the excess point and lattice defects generated by plastic deformation. The amorphization by MA starting from powders of crystalline intermetallics is attributed to the accumulation of point and lattice defects which raise the free energy of the faulted intermetallic above that of the amorphous alloy.

The science and technology of mechanical alloying

Abstract: Mechanical alloying (MA) is a powder metallurgy processing technique involving cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill, and has now become an established commercial technique to produce oxide dispersion strengthened (ODS) nickel- and iron-based materials. MA is also capable of synthesizing a variety of metastable phases, and in this respect, the capabilities of MA are similar to those of another important non-equilibrium processing technique, viz., rapid solidification processing (RSP). However, the “science” of MA is being investigated only during the past 10 years or so. The technique of mechanochemistry, on the other hand, has had a long history and the materials produced in this way have found a number of technological applications, e.g., in areas such as hydrogen storage materials, heaters, gas absorbers, fertilizers, catalysts, cosmetics, and waste management. The present paper discusses the basic mechanisms of formation of metastable phases (specifically supersaturated solid solutions and amorphous phases) by the technique of MA and these aspects are compared with those of RSP. Additionally, the variety of technological applications of mechanically alloyed products are highlighted.