Thermal-spray technology is commonly used for structural components by building up a protective coating layer on their surfaces. Choosing a suitable sprayed metal can improve corrosion resistance, [1,2] oxidation resistance, [3±5] wear resistance [6] and/or heat insulation, and thus extend the life of protected components.Three methods have been developed to give a protective coating to resist oxidation: glass-ceramic coating, [7±11] aluminiding the surface by reaction between Al and metal substrates, [12±15] and over-layer coating such as MCrAlY (M=Fe, Co, Ni) superalloys. [16±21] Glass-ceramic or aluminide layers are hard and brittle at low temperatures, and easily delaminated from the substrate due to the mismatch of the coefficient of thermal expansion. Over-layer coating of MCrAlY alloys is the favorite one for industry to protect structural components from oxidation at high temperatures. However, its lower hardness, about HRC 20~30, renders them poor in wear resistance when particulates or counterparts are involved in the environment. Thus, traditional coating materials can not provide an ideal coating both for oxidation resistance and wear resistance. In this study, a new alloy design concept ª;multi-principle-element alloysº, was explored to create alloys with excellent combinations of properties for some critical applications such as dies, molds and turbine blades. Processing, microstructure and properties were investigated to evaluate such multi-principle-element alloys as AlSiTiCrFeCoNiMo 0.5 (designated as 8E) and AlSiTiCrFeNiMo 0.5 (designated as 7E).As-cast microstructure and properties: Figure 1 shows the XRD patterns of as-cast 8E and 7E alloys. It reveals that their microstructures consist primarily of an ordered BCC phase and two FCC phases. The ordered BCC phase of 8E alloy had a lattice constant a = 2.87 , and the two FCC phases had a = 3.52 and 4.14 , respectively. 7E alloy had the phases with nearly the same constants as 8E alloy. It is indeed a surprise to see that these alloys did not to have many complex phase constituents since many possibilities of binary or ternary phases might be expected for such a large number of principle elements. Figure 2 shows the SEM pictures of the as-cast microstructures of 8E and 7E alloys. They were of a typical dendritic cast structure. EDS analysis indicates that Si, Ti, Cr, Fe, and Co and Mo were the main elements in the dendrite whereas Ni and Al were the main elements in the interdendrite regions. It is interesting to see that Co played as a neutral element and partitioned almost equally in both regions. The dendrite phase corresponded to the BCC phase shown in the XRD pattern and the interdendrite one was related with the FCC phases since the former was rich in Mo and Cr elements both of which have the BCC structure and are the first two elements highest in melting point. COMMUNICATIONS 74

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AlCrNbSiTiV nitride films were deposited by reactive radio-frequency magnetron sputtering and the effects of substrate bias on the chemical composition, structure and mechanical properties of the deposited films were investigated. AlCrNbSiTiV nitride films exhibit a single FCC NaCl-type structure and have the stoichiometric nitride ratio of (Al, Cr, Nb, Si, Ti, V)50N50. The deposition rate decreases with increasing substrate bias due to resputtering effects and densification of films, which also leads to less obvious columnar structure, reduced grain size, smaller surface roughness and transition of preferred orientation from the (1 1 1) plane to the (2 0 0) plane. The nitride film deposited at −100 V exhibits the maximum compressive stress around 4.5 GPa and attains a peak hardness and an elastic modulus of 42 GPa and 350 GPa, respectively, which fall in the superhard grade. Moreover, the film keeps its hardness at the superhard grade even after its residual compressive stress was partially released by annealing at 1073 K for 5 h. The structural evolution mechanism and strengthening mechanism are both discussed.