ISSN 0018-151X, High Temperature, 2014, Vol. 52, No. 1, pp. 19–25. © Pleiades Publishing, Ltd., 2014. 19 1 INTRODUCTION Plasma spray is one of the most significant tech- niques employed to develop coatings of both refracto- ry metals and ceramics. The main advantages of plas- ma spray technique include the formation of ceramics with fine, equi-axed grains without columnar defects at high deposition rates. It is a typical thermal spray- ing process that combines particle melting, quenching and splat formation in a single operation [1, 2]. To en- sure better adhesion, it is a wide practice to blast the surface of the substrate with sand grit. At blasting angle of 90° and spraying angle of 90°, better adher- ence has been reported than at any other blasting or spraying angle [3]. The microstructure of plasma sprayed cermet coatings is found to be inhomoge- neous [4]. Within the lamellae, it has a columnar struc- ture. The size of the splats lies in between 10–100 μm in diameter and 1–3 μm in thickness. R. McPherson [5] has reported that coating over the substrate has both columnar and equiaxed microstructure. The coating produced by plasma spray technique may have several applications in aerospace industry. For example, it can increase the shelf life of the turbines which are conti- nuously exposed to high temperature environment [6, 7]. Similarly, various automobile parts like piston crown, piston ring, cylinder block and turbocharger components etc. can also be coated to protect them from wear. It is reported by F. Rastegar and A.E. Craft [8] that plasma sprayed molybdenum/chromium carbide coatings have higher wear resistances than electroplat- 1 The article is published in the original. ed molybdenum carbide coatings. Molybdenum has high melting point of 2623°C and hardness of 5.5 in Mohs scale [9]. It forms MoO 2 in the plasma zone which is a well known anti-friction material. MoO 2 has lower coefficient of friction than that of pure molybdenum. It also has the ability to prevent expan- sion and softening in extreme temperature environ- ment. Similarly, titanium nitride has a melting point of 2930°C with high hardness, low coefficient of friction, and excellent wear resistance. It protects cutting and sliding surfaces from getting damaged [10–16]. In the present work, molybdenum premixed with titanium nitride was sprayed using a plasma torch on Al-Si al- loys to obtain requisite hardness and adhesion strength of the coatings with an objective to find a suitable coat- ing for the turbine blades and casing of the turbo- chargers mostly found in diesel vehicles. Generally, the turbocharger turbine blades and casing are made of Al–Si alloy. The components get worn out due to high temperature exhaust gases as well as abrasive par- ticles present in engine oil, thereby, do not last the specified operating life. The blades get fully damaged before the specified operating life. The objective of this investigation is to coat the blades with molybde- num premixed with titanium nitride powder to en- hance its hardness and adhesion strength, so that it provides the required wear resistance at high tempera- ture. Four different compositions of molybdenum and ti- tanium nitride powders (100% Mo, 95% Mo + 5% TiN, 90% Mo + 10% TiN and 85% Mo + 15% TiN) were pre- pared and coated at four different power levels on the Improvement of Microstructural and Mechanical Properties of Plasma Sprayed Mo Coatings Deposited on Al–Si Substrates by Pre-mixing of Mo with TiN Powder 1 D. Debasish, S. Mantry*, D. Behera, and B. B. Jha CSIR-Institute of Minerals and Materials Technology, Bhubaneswar-751013, India *e-mail: mantrysisir@gmail.com Received December 27, 2012 Abstract—The present work embodies development of a new class of mechanically improved Mo-TiN coat- ing material using plasma spray technique. The coatings are developed on Al–Si alloy at different torch input power levels ranging from 15 kW to 30 kW. Pre-mixing of TiN with molybdenum enhances adhesion strength and hardness of the coatings. Maximum adhesion strength of 22 MPa (± 0.75) and hardness of 748 HV (±30) are found for the coating when molybdenum is pre-mixed with 10% TiN. FESEM micrographs of the as- sprayed coatings showed formation of plate-like structures of splats which indicates TiN sites as reinforce- ment in Mo matrix. X-ray diffraction study reveals the formation of both MoO2 and TiN as minor phases in the coating microstructure. The significant enhancement of mechanical properties like adhesion strength and hardness is attributed towards the presence of these phases. DOI: 10.1134/S0018151X14010076 PLASMA INVESTIGATIONS