Oxidation of nickel-molybdenum coatings on diamond

Conclusions The main processes causing oxidation in air of pure and nickel-alloyed molybdenum coatings on diamond are: build up of oxides in the scale; removal of molybdenum and carbon in the composition of volatile oxides MoO₃ CO, and CO₂; renewal of the carbide layer on the boundary with the diamond as a result of the oxidation-reduction reactions taking place in this zone; enrichment of the scale with nickel as a result of selective oxidation of the molybdenum-nickel phases which reduces the rate of removal of molybdenum from MoO₃. The contribution of each component is determined by the oxidation conditions and the nickel content of the molybdenum coatings. The described mechanisms make it possible to predict the behavior of components made of molybdenum metallized diamond powders under specific service conditions.Translated from Poroshkovaya Metallurgiya, No. 4(340), pp. 53–58, April, 1991.     

Formation of chromium-copper coatings on diamond

The mechanism of chromium and chromium-copper formation is determined, which is mainly by transfer of metal ions to the reaction surface (of diamond) and carbon diffusion (from diamond) into the coating. Introduction of copper oxides into the chromium metallizer promotes an increase in coating thickness due to the additional contribution to transfer of chromium of CuO, Cu, and CrO. With reduction of copper oxides this contribution is reduced, which gives rise to a slower coating thickness growth rate. Slower growth is also caused by accumulation in the metallizer of chromium oxides and carbides which block evaporation as well as inhibiting diffusion of carbon into the body of the coating.     

Formation of chromium coatings alloyed with nickel on diamond

The methods of x-ray phase analysis are used to study the composition of chromium — nickel coatings and metallizing mixtures (metal spraying compositions) as a function of the annealing conditions. The thickness of the coatings is calculated from the weight gain by diamond. It is shown that coatings are formed mainly by the transfer of chromium and nickel through the gas phase to the reaction surface (diamond or the outer surface of the coatings) and diffusion of carbon from the diamond (into the coating) which determines the phase composition of the coating: Cr₃C₂, Cr, Cr₇C₃, and Ni. Nickel appears in the metal spraying compositions because of the reduction of NiO by the carbon of chromium and carbon monoxide. The formation of the phases in the metal spraying compositions, which block the intensity of evaporation of chromium (due to NiO restoration with chromium) and of Ni(Cr) (due to the dissolution of chromium in nickel), is the factor that limits the growth of the coating. This is the main reason for the decrease in the thickness of the coating when nickel monoxide is added to the chromium metallizing mixture.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 1 (361), pp. 47–51, January, 1993.     

含Si金刚石涂层的工艺研究

利用微波等离子体辅助化学气相沉积的方法,以H₂、CH₄和D₄(八甲基环四硅氧烷)为沉积先驱物,探索了一种在硬质合金基底上制备出含Si元素的金刚石涂层的新工艺.试图利用这种新的方法,进一步提高金刚石涂层对硬质合金基底的附着力.实验结果表明:当D₄的流量相对CH₄的流量较大时,得到球团状的胞状组织;只有当D₄和CH₄的流量相当的情况下,才能沉积出质量较好的金刚石涂层,同时又含有少量的Si使金刚石涂层的附着力较好.     

金刚石颗粒表面镀铜层的控制氧化

为了改善熔融玻璃对金刚石颗粒的润湿,需要对镀铜金刚石颗粒在一定气氛下进行控制氧化,从而在其表面获得一定厚度的Cu₂O层.通过对金刚石颗粒表面镀铜层氧化的热力学计算,确定了在650℃、露点温度为20℃的N₂/H₂O二元混合气氛中进行氧化.氧化的动力学研究表明,在此条件下金刚石颗粒表面镀铜层的氧化符合抛物线规律,其抛物线速度常数为1.127 5×10^-12g²·cm^-4·min^-1.在动力学研究的基础上,本实验选择氧化时间为40 min.XRD实验结果表明,氧化后的金刚石颗粒表面只有Cu和Cu₂O,未生成CuO.     

X-ray diffraction investigation of Ni-Mn-Sn-Ti coatings applied to diamond

Conclusions At the boundary with diamond there forms a carbide interlayer consisting mainly of Mn₇C₃, which ensures a strong bond between the coating and diamond. In the case of a titanium-containing coating, titanium carbide and oxycarbides forming as a result of the dissolution of oxygen adsorbed on the surfaces of metal powder particles do not occur at the boundary of the coating, but are distributed within it. This helps purify the system from oxygen and intensifies the reaction of the melt with the diamond.Translated from Poroshkovaya Metallurgiya, No. 1(253), pp. 40–44, January, 1984.     

镀层对金刚石/玻璃复合材料性能的影响

为满足现代电子工业日益增长的散热需求,急需研究和开发新型高导热陶瓷（玻璃）基复合材料,而改善复合材料中增强相与基体的界面结合状况是提高复合材料热导率的重要途径.本文在对金刚石和镀Cr金刚石进行镀Cu和控制氧化的基础上,利用放电等离子烧结方法制备了不同的金刚石增强玻璃基复合材料,并观察了其微观形貌和界面结合状况,测定了复合材料的热导率.实验结果表明：复合材料中金刚石颗粒均匀分布于玻璃基体中,Cu/金刚石界面和Cr/Cu界面分别是两种复合材料中结合最弱的界面;复合材料的热导率随着金刚石体积分数的增加而增加;金刚石/玻璃复合材料的热导率随着镀Cu层厚度的增加而降低,由于镀Cr层实现了与金刚石的化学结合以及Cr在Cu层中的扩散,镀Cr金刚石/玻璃复合材料的热导率随着镀Cu层厚度的增加而增加.当金刚石粒径为100μm、体积分数为70%及镀Cu层厚度为约1.59μm时,复合材料的热导率最高达到约91.0 W·m^-1·K^-1.     

Cladding diamond powders by thermodiffusion saturation. I. Kinetics of formation of metallic coatings on the surface of diamond

Translated from Poroshkovaya Metallurgiya, No. 6(318), pp. 53–56, June, 1989.     

Oxidation and corrosion resistance of TiAl3 coatings

Titanium aluminides based on TiAl, TiAl₃ and Ti₃Al are potential materials for high temperature aerospace applications. Their low density, high temperature creep resistance, high temperature strength and high oxidation resistance make them excellent coating materials. However these coatings are likely to be subjected to high temperature and corrosive environments during service. Hence it is aimed to study the oxidation and corrosion resistance of TiAl₃ coatings on various types of substrates. In the present work, TiAl₃ is coated on high speed steel, stainless steel 304, stainless steel 316, copper and aluminum substrates by physical vapor deposition technique. X-ray diffraction analysis confirms the presence of TiAl₃ phase. The hardness studies reveal that better hardness can be achieved with thick coatings. The oxidation behavior of the coatings is studied by carrying out step stress experiments at elevated temperatures. Coated samples are heated up from 400°C in the steps of 100°C for 1h in each step to 1000°C. The mass gain caused by oxidation was determined. The oxidation curve drawn as a function of mass gain versus temperature reveals that TiAl₃ film started to oxidize above 800°C, where as oxidation of the uncoated substrates began at a much lower temperature of 550°C. The excellent oxidation resistance of the coatings can be attributed to the formation of an amorphous Al₂O₃ film. Scanning electron microscope (SEM) and EDAX analysis confirm the presence of an amorphous Al₂O₃ film. The corrosion behavior of TiAl₃ coatings are investigated by the polarization resistance experiments in NaCl aqueous solution at ambient temperature. According to the Tafel plot analysis, the coatings show lower corrosion rate than the untreated substrates. The major corrosion in the coatings arose from electrolyte penetration into the pores of the coatings. In fact, a dense coating showed a high corrosion resistance in an aqueous medium.     

Special features of formation of molybdenum coatings on diamond with the spatial distribution of reagents

Translated from Poroshkovaya Metallurgiya, No. 4(304), pp. 62–65, April, 1988.     

夹杂物对Cr-Ni系高强度钢耐蚀性能的影响

对比研究了2种Cr-Ni系高强度钢在人造海水条件下耐蚀性能差异,采用ASPEX自动扫描电镜分析了钢中夹杂物种类、数量和分布,利用金相显微镜对夹杂物引发腐蚀的过程开展了原位分析,并利用扫描电镜(SEM),观察了腐蚀后样品的微观形貌。全浸腐蚀实验结果表明,A钢虽然合金含量较高,但其腐蚀速率要大于B钢;夹杂物分析及其原位腐蚀实验研究表明,B钢通过Ca处理获得了良好的夹杂物改性效果,将钢中对耐蚀性提高不利的MnS夹杂物改性为CaS复合夹杂物,降低了B钢的点蚀敏感性,提高了B钢的耐蚀性能。     

铬镍生铁在不锈钢生产中的应用

通过对铬镍生铁性质的分析,提出铬镍生铁不同的镍含量、硅含量和不同的磷含量对应的使用方法不同。并简单说明了当前铬镍生铁使用的影响。