A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties

Powder metallurgy (PM) of titanium is a potentially cost-effective alternative to conventional wrought titanium. This article examines both traditional and emerging technologies, including the prod...

https://www.tandfonline.com/doi/pdf/10.1080/09506608.2017.1366003

Powder metallurgy of titanium – past, present, and future

Nanostructured (i.e., 1–200 nm grain size) and ultrafine-grained (i.e., 200–500 nm grain size) metals are of interest, not only as a result of their unusual combinations of physical and mechanical properties, but also because they can be readily synthesized using well-developed synthesis techniques. Cryomilling, i.e., mechanical alloying in liquid nitrogen, is representative of a class of synthesis techniques that attain the nanostructured state via severe plastic deformation. In this overview, published data related to cryomilled materials are reviewed and discussed with particular emphasis on cryomilling mechanisms; microstructure and thermal stability of cryomilled powders; primary consolidation and secondary processing methods; microstructural evolution during consolidation; and mechanical response of consolidated materials. The deformation behavior and the underlying mechanisms that govern cryomilled materials are discussed and compared with those of nanostructured materials processed via other methods, in an effort to shed light into the fundamental behavior of ultrafine-grained and nanostructured materials.

Cryomilled nanostructured materials: Processing and properties

Advances in metals and alloys for joint replacement

The morphological and microstructural changes during mechanical milling of Al powder mixed with 5 vol% nanoscaled alumina particles (35 nm) were studied. The milling was performed in a planetary ball mill under argon atmosphere for various times up to 24 h. The process was also conducted for Al and Al–5 vol% Al 2 O 3 (1 μm) powders to explore the role of reinforcement nanoparticles on the mechanical milling stages. The results showed that the addition of hard particles accelerate the milling process, leading to faster work hardening rate and fracture of the aluminum matrix. Meanwhile, the structural evolution during mechanical milling of the microcomposite powder occurred faster than that of the nanocomposite powder. The result of X-ray diffraction analysis by Williamson–Hall method determined that the so-called crystallite size and lattice strain of the Al matrix of nanocomposite are smaller than that of the microcomposite. Meantime, the particle size distribution and bulk powder density of the two composites were found to be rather equal after 20 h milling, but they were significantly different from those of the unreinforced Al. The mechanisms of mechanical milling for the reinforced and unreinforced Al powders are addressed with stressing on the role of alumina particles.

Structural evolution during mechanical milling of nanometric and micrometric Al2O3 reinforced Al matrix composites

In this paper we try to summarize the research activities of the PM group in the University Carlos III of Madrid. This research group is highly devoted to PM activities covering different fields (both under the point of view of the materials and the processes). In the PM lab powders can be produced by spray pyrolysis, mechanical alloying and water/gas atomization. These powders can be processed by pressing and sintering, powder injection moulding, isostatic pressing,… Sintering facilities cover vacuum and gas controlled sintering. Regarding the materials, in the group we have different research lines covering low alloyed steels, stainless steels, HSS, ferrites, metal matrix composite (Al and Fe base), Ti, intermetallics, ceramics with functional and structural propierties, … In this paper we describe slightly some of the recent developments produced in the group which is not exhaustive (are there a few more) but representative about we are doing at present.

New Developments in Powder Technology

A ferritic stainless steel has been manufactured through the powder metallurgy (P/M) route: uniaxial pressing and sintering. The sintering process was carried out in vacuum, at 1215 °C for 30 min. After sintering, materials showed nearly 90% of density. A complete metallographic study was carried out using optical microscopy and scanning electron microscopy (SEM). Wear behavior was evaluated using a “pin on disk” test according to ASTM Standard G99. Eight test conditions were studied, varying the load (5 and 10 N), the speed (0.1 and 0.4 m/s), and the counter-material (chromium steel and a martensitic stainless steel). The sliding distance was 400 m, and tests were carried out on polished materials, with less than 30% of relative humidity. Moreover, wear tracks were observed by SEM in order to understand the wear processes involved, which depend mainly on the counter-material.

Wear Behavior of a Ferritic Stainless Steel with Carbides Manufactured through Powder Metallurgy

Ti-3A1-2.5V alloy was originally developed for the fabrication of hydraulic and fuel structures in conventional airplanes because it has intermediate performances (i.e. mechanical and corrosion resistance) compared to titanium and Ti-6A1-4V. The production of structural titanium components via powder metallurgy has been lately considered and a lot of interest has been shown from the aerospace industry due to the development of novel production methods which avoid the presence of chlorides. In this work the production and characterisation of the Ti-3A1-2.5V alloy produced considering the blending elemental approach is assessed. The alloy is consolidated by two conventional powder metallurgy routes (pressing and sintering and hot-pressing) in order to study the effect of the processing parameters. Complete diffusion of the alloying elements and homogeneous microstructures are generally achieved. The mechanical performances of the sintered products, which are comparable to those of the wrought alloy, are correlated to the relative density and microstructural features.

On the Microstructure and Properties of the Ti-3Al-2.5V Alloy Obtained by Powder Metallurgy

Titanium alloys are ideal for a great range of engineering applications; however, their high manufacturing costs hinder their widespread use. This study investigates the relationship between the processing and properties of representative Ti-based materials manufactured via powder metallurgy in order to reduce the manufacturing costs. This is possible as powder metallurgy techniques are near-net shape processes with high yield of material. It is found that the relative density increases with the sintering temperature, and it is slightly higher for longer processing times, reaching values in the 94–97% range. Moreover, homogeneous microstructures are obtained for all the conditions investigated, achieving an equiaxed microstructure for Ti and the typical lamellar structure for the Ti-6Al-7Nb alloy. However, the increment of the temperature also leads to a higher amount of interstitial pick-up, with a maximum increment of 0.21 wt.% and 0.028 wt.% for oxygen and nitrogen, respectively. The highest properties achieved for Ti and Ti-6Al-7Nb are 272 HV (hardness), 17.9 W/m·K (thermal conductivity), and 62.7 μohm·cm (electrical resistivity) and 336 HV, 6.9 W/m·K, and 180 μohm·cm, respectively.

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Relationship between Manufacturing and Properties of Vacuum Sintered Ti and Ti-6Al-7Nb

The increasing demand of PM parts for automobile and aerospace applications has caused a strong development of the aluminium based metal matrix composites (MMCs).Aluminium alloys are one of most widely used materials as matrix in MMCs, both in research and development as well as in industrial applications. The main reason is the combination of good specific properties, the first requirement in most applications, and the competitive price compared to other low density alloys such as Mg or Ti alloys. In the present work, the influence of the ceramic reinforcement addition to a 2xxx series aluminium alloy is studied. Several percentages of TiCN have been added to the Al-Cu alloy using PM techniques, in order to analyze its influence on the liquid phase sintering process and also on the final properties of the material. The materials have been uniaxially compacted using two different pressures to determine the optimal pressing condition. They have been subsequently sinterized in a N2-H2 atmosphere. Analysing the results obtained, it can be concluded that the addition of TiCN allows a better distribution of the liquid phase up to the 10 %wt, where the optimal results are observed: For higher quantities of reinforcement, elemental copper is observed in the microstructure with the consequent decrease in densification.

Elisa Maria Ruiz-Navas

Papers

New Developments in Powder Technology

Wear Behavior of a Ferritic Stainless Steel with Carbides Manufactured through Powder Metallurgy

On the Microstructure and Properties of the Ti-3Al-2.5V Alloy Obtained by Powder Metallurgy

Relationship between Manufacturing and Properties of Vacuum Sintered Ti and Ti-6Al-7Nb

Study of TiCn additions to an 2xxx series aluminium alloy