TiN-TiB2 composite coatings reactively produced by electrothermally exploded powder spray

Composite coatings composed of titanium nitride, TiN, and diboride, TiB₂, were reactively produced by the electrothermally exploded powder spray technique, in which feedstock powder was prepared from titanium and boron nitride particles. The microstructure of the coating was composed of titanium-ceramic particles the size of which were on the order of several nanometers to a few hundred nanometers. Such reactive thermal spraying brought base-metal saturation into a coating layer at the early stages of coating formation. The ceramic composite spray using feedstock of TiN and TiB₂ particles preferentially brought a new phase of cubic titanium boronitride together with TiN and TiB₂ into a coating. On comparing such a coating to one produced by the conventional method, the reactive thermal spray coating was richer in TiN and TiB₂ due to the excess nitrogen in the feedstock.     

Zirconium boride and tantalum carbide coatings sprayed by electrothermal explosion of powders

Refractory zirconium diboride and tantalum monocarbide ceramic powders were sprayed using an electrothermal explosion caused by a high-voltage electric breakdown and large-current discharge heating. This spray technique was improved using a purpose-designed powder container, which made it possible to melt the powder completely and accelerate it to impinge on substrates. The electrical energy applied to the powder was estimated to be about twice the energy theoretically needed to melt just the powder. Although the ceramics used in this work are hard-sintered materials by nature, they could be sprayed and deposited to form coatings on metal substrates without additives and sintering agents. The coatings formed exhibited no chemical decomposition in the boride, and only small amounts of decarburization in the carbide due to its nonstoichiometry. The tantalum carbide coating mixed with iron and aluminum substrates in the range of 10 μm to several tens of micrometers.     

Reactive thermal spray by high velocity ceramic jet and characterization of the coatings

A ceramic jet composed of molten particles in an electrothermally exploded powder spray was identified by the flash, soft x-ray radiography technique. The velocity of the leading edge of the jet was estimated to be 900 m/s. The coating obtained by a ceramic jet of titanium diboride consisted of a mixing layer of the substrate material and sprayed ceramics. A coating, which exhibited no pores or cracks, was formed through the dense deposition and solidification of spray droplets. The successive impacts of the droplets caused melting and stirring of the substrate surface to form a mixing layer. Some of these layers were formed due to capillary movement of the molten substrate material into the fractures of coarse ceramic particles. Thermal spray by chemical reaction between titanium and boron nitride particles resulted in a composite coating of TiN and TiB₂. The character of the mixing layer indicated that the depth profiles depended on the substrate material.     

Generation of a high-velocity jet in the electrothermal explosion of conductive ceramic powders

The electrothermal explosion spraying of conductive ceramic powders was characterized according to the electric and gas dynamic behavior of heated powders. Optical observation revealed the generation of the jetting with a leading velocity over 3 km/s. The velocity depended on the shape of the jet and the energy supplied to the powder. The heating process was related to the jetting process of the heated powders. The total electric energy supplied to the powder was two to three times the theoretical amount needed to melt the powder. Such electric energy was used for heating and accelerating the powder. This spray technique is characterized with the high-velocity jet consisting of high-pressure gas and molten ceramic particles.     

Sliding wear behavior of tungsten carbide thermal spray coatings for replacement of chromium electroplate in aircraft applications

Tungsten carbide (WC) thermal spray coatings have gained increased acceptance for commercial aircraft applications driven by the desire to replace chromium electroplate due to environmental and economic considerations. In order to confidently replace electroplated chrome with WC thermal spray coatings in aircraft applications, the coatings must demonstrate fatigue and wear characteristics as good as or better than those of electroplated chrome. Previous research in this area has shown that the fatigue life of the WC thermal spray coatings can be improved by inducing compressive residual stresses in the coating. This paper compares the wear characteristics of several types of WC thermal spray coatings with those of electroplated chrome in sliding wear tests using the “block-on-ring” procedures described in the ASTM G77 standard. Wear results are interpreted in terms of coating residual stresses and in terms of x-ray diffraction (XRD) and scanning electron microscope (SEM) analyses.     

氩弧熔敷Ti-Si-C系陶瓷涂层中物相的热力学预测

利用热力学原理推导出反应焓和反应吉布斯（Gibbs）自由能与温度的关系式.根据Ti-Si-C系相图,对用钨极氩弧（TIG）热在钛合金表面熔敷形成涂层过程中可能的12个化学反应进行热力学分析.热力学计算得出,Ti元素能与SiC,Si及C元素反应生成TiC,Ti₃SiC₂相和Ti₅Si₃,TiSi₂金属间化合物.理论分析结果表明,在TIG熔敷条件下,通过改变不同的原材料初始组成,可以采用热力学分析方法预测熔覆层的物相组成.试验结果表明,预测结果与试验结果符合得很好.     

Behavior of porosity and copper oxidation in W/Cu composite produced by plasma spray

A spherical tungsten (W)/copper (Cu) composite powder was plasma-sprayed onto a boron-nitride-coated graphite substrate to produce heat sink material for the electronic packaging by atmospheric plasma spray using different input powers. At the surface of the deposited layer, Cu became oxidized to cuprite (Cu₂O). The degree of oxidation at the surface layer did not vary significantly with input power. Very little Cu₂O was detected at the inner layers after grinding off the 70 μm from the surface. The input powers had a strong effect on the porosity in the deposit layers. The porosity in the deposit layers at 25 kW was very small, about 3 vol%. The microstructures of W/Cu composite were discussed.