A method for predicting the nucleation kinetics of gas-atomized droplets has been developed by combining models predicting the nucleationtemperature of cooling droplets with a model simulating the droplet motion and cooling in gas atomization. Application to a Sn–5 mass%Pballoy has yielded continuous-cooling transformation (CCT) diagrams for the heterogeneous droplet nucleation in helium gas atomization. Bothinternal nucleation caused by a catalyst present in the melt and surface nucleation caused by oxidation are considered. Droplets atomized at ahigh atomizing gas velocity get around surface oxidation and nucleate internally at high supercoolings. Low atomization gas velocities promoteoxidation-catalyzed nucleation which leads to lower supercoolings. The developed method enables improved screening of atomized powders forcritical applications where stringent control of powder microstructure is required.

FeNiN thin films with good soft magnetic properties were synthesized on Si (1 0 0) substrates at 473K by RF magnetron sputtering.The dependence of phase structure and magnetic properties on nitrogen partial pressure, nickel concentrations, film thickness andsubstrate temperature were systematically investigated. The phase evolution from a-(Fe,Ni)N to x-(Fe,Ni)2N with increase of nitrogenpartial pressure was seen. The addition of Ni caused FeNiN films to turn from BCC structure to FCC structure. Clear reproduciblestriped domains appeared at the film surfaces when XNi 19.6%, which is explained by the high enough perpendicular anisotropy andthe small stress in the film. All films show smooth surfaces and good soft magnetic properties compared to corresponding FeNcompounds. The magnetic properties depended dramatically on the phase structure. Optimum soft magnetic properties with HC ofo1 Oe are obtained between 5.0%pXNip10.0%.

A model was developed that permits computation of CCT diagrams for surface oxidation catalyzed heterogeneous nucleation of alloy dropletsfrom a few experimental data. The model addresses the progress of droplet surface oxidation during continuous cooling in terms of oxidenucleation and growth kinetics. Avrami-corrected surface oxidation kinetics are adopted to account for the impingement of oxide islands growingon the droplet surface during continuous cooling. The model predicts droplet nucleation kinetics in relation to the oxidation potential in theatmosphere, droplet diameter, cooling schedule and four temperature-independent constants. CCT diagrams were computed for Sn-5 mass%Pbdroplets cooling in nitrogen atmospheres with various oxidation potentials using nucleation data and cooling simulation of traveling mono-sizedroplets. Calculated CCT diagrams show that droplet surface oxidation sharply increases the droplet nucleation temperature particularly at highcooling rates. Computation can be extended to predict CCT curves for droplet nucleation in industrial thermal spraying processes.

Fe–N thin films were fabricated on Si (1 0 0) by RF magnetron sputtering. The dependence of the structural andmagnetic properties with varied nitrogen partial pressure ePN2 T; RF power and film thickness were systematicallystudied. The phase evolution from a-Fe(N) to x-Fe2N with increase of nitrogen partial pressure was seen. a00-Fe16N2existed in the whole range of the nitrogen partial pressure. The research of in-plane magnetic anisotropy with differentnitrogen partial pressure indicated that interstitial nitrogen atoms affected in-plane magnetic anisotropy in Fe–Nsystem. With the increase of the film thickness from 50 to 730 nm, the saturated magnetization (Ms) decreases and thecoercive force (Hc) increases. The good soft magnetic properties withMs of 2223 emu/cm3 and Hc of 4 Oe were obtainedat the optimized parameters of PN2; RF power and film thickness.

Nickel-based and tungsten carbide (WC) composite coatings were prepared by laser cladding under different laser beam powers.The microscopic morphology and distribution of WC particles in a laser-clad Ni–WC coatings were characterized by scanning electronmicroscopy (SEM). Two effective methods to avoid the stress concentration and cracks were used. One is the gradient coating with WChard phase varied gradually from the substrate to the top of the coating using three-step laser cladding. The other is the coating whereWC particles, with a marked gradient distribution at interface between the matrix and WC, were uniformly incorporated in the coating byoptimizing WC particle concentration, laser power and thickness of the layer. The wear test results show that three-step laser-clad gradientlayer is not recommended especially for long-term wear applications because of the complicated laser processing and poorer interfacebetween the matrix and WC particles.