Cold Sprayability of Mixed Commercial Purity Ti Plus Ti6Al4V Metal Powders
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Cold Sprayability of Mixed Commercial Purity Ti Plus Ti6Al4V Metal Powders Huseyin Aydin1 • Mashael Alomair1 • Wilson Wong1 • Phuong Vo2 Stephen Yue1
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Submitted: 1 May 2016 / in revised form: 14 November 2016 / Published online: 30 January 2017 ASM International 2017
Abstract In the present work, metallic composite coatings of commercial purity Ti plus Ti6Al4V were produced by cold spraying to explore the effect of mixing on porosity and mechanical properties of the coatings. The coatings were deposited using N2 gas at 800 C and 4 MPa pressure on 1020 steel substrate. Coating characteristics were studied by examining porosity percentages and Vickers’s hardness. The microstructure was examined using optical and electron microscopy techniques. It was observed that mixing metal powders can lead to improvements in cold sprayability, specifically decreases in the porosity of the ‘matrix’ powder. It is shown that a critical addition can significantly influence porosity, but above this critical level, there is a little change in porosity. Hardness differences between the two powders are considered to be the first-order influence, but differences in particle sizes and morphology may also be contributing factors. Keywords cold spray deposition efficiency mixed metal powders coating porosity
Introduction Over the last few years, cold gas dynamic spraying, which is an important part of the thermal spray coating family, has become an emerging manufacturing and repair technology, particularly in the aerospace industry. This & Huseyin Aydin [email protected] 1
Department of Mining and Materials Engineering, McGill University, Montreal, QC, Canada
2
National Research Council, Boucherville, QC, Canada
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technique enables production of various coatings, such as pure metals, alloys, composites, nanostructure materials, and even amorphous materials. It is an all-solid state, high kinetic energy, coating, and a free-form fabrication process that uses high-pressure compressed gas to propel solid particles of diameters between 10 and 50 lm onto a substrate under atmospheric conditions (Ref 1, 2). In general, for a given set of powder characteristics (i.e., composition, microstructure, and morphology, size and size distribution) and substrate combination, increasing the spray process intensity (i.e., the gas temperature and pressure) will definitely increase the deposition efficiency (DE) and possibly decrease the porosity, primarily because the particle velocity is increased (Ref 2-5). However, coldsprayed pure titanium and Ti6Al4V coatings are reported to be quite porous even at very high particle velocities, although deposition efficiencies are close to 100% (Ref 6, 7). In the cold spray literature, there are many examples of mixing metal powders with ceramic powders (Ref 6-11), which illustrates the main reason for mixing powders— creating materials with improved or novel properties. In 1995, Buzdygar et al. (Ref 12) was granted a patent describing the method of producing a coating using c
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