Internal-Carburizing Behavior of Ni-V,Ni-Cr,and Ni-3Nb Alloys

Ni-2V, Ni-5V, Ni-12V, Ni-10Cr, Ni-20Cr, andNi-3Nb alloys were carburized in 1.5 v/oC₃H₆ (bal. H₂) over therange 700-1000°C. Carburization of Ni-5V, Ni-12V,Ni-20Cr, and Ni-3Nb obeyed the parabolic rate law. Ni2V and Ni-10Cr, however, formed onlythin carbide scales upon carburizing. Carburizationrates decreased with increased vanadium content fromNi-5V to Ni-12V for all exposure conditions. V4C3 formed throughout the reaction zones of Ni-12V.Cr₃C₂ formed in the surfaceregions and Cr₇C₃ formed withinthe interior of Ni-20Cr. NbC precipitated in Ni-3Nbunder all conditions. The precipitate morphology changed with temperature and distance from thegas-metal surface. V₄C₃ andCr₃C₂ particles were generallysmall and spheroidal near the surface of Ni-12V andNi-20Cr, respectively, increasing slightly in size with distance from the surface and withincreasing temperature. The vanadium and chromiumcarbides formed intergranular networks toward thereaction fronts. The NbC precipitates were generallylarge and became Widmanstatten at increasing distancewithin the carburized zone of Ni-3Nb. Expressions forthe diffusion coefficient of carbon in nickel from themeasured permeabilities and carbon solubility data were determined. Solubility products weredetermined for all of the carbides formed and found tobe large in comparison with the product of theactivities of the precipitate elements. Wagner's theory of internal oxidation was shown to be anapproximation to the carburization kinetics attemperatures of 900°C or higher.     

Tribocorrosion behaviour of overlay welded Ni-Cr 625 alloy in sulphuric and nitric acids: Electrochemical and chemical effects

The tribocorrosion behaviour of overlay welded Ni-Cr 625 alloy sliding against alumina in 0.5 M H₂SO₄ and 0.5 M HNO₃ solutions under potentiostatic conditions was investigated. The passivation of the samples in the two electrolytes at different potentials (−1.5, −0.3 and +0.3 V_MSE) was studied by means of potentiodynamic polarization curves and XPS. The tribocorrosion behaviour of the alloy in sulphuric acid was similar to the behaviour of stainless steels found in other studies, with much lower wear at cathodic potential compared to passive conditions. However, the behaviour in nitric acid was highly influenced by the reduction of nitric acid at the electrode-electrolyte interface. This reaction leads to the oxidation of the alloy even at cathodic potential. This feature influenced the tribocorrosion properties of the alloy in nitric acid, the wear rate at cathodic potential being in the same range as at passive potentials.     

Importance of the Casting Process. Comparative Survey of the Commonly Used Ni-Cr Dental Alloys

Mobile or fixed dental prostheses are a common and important part of life. Many noble metal-based alloys have been used in prosthodontics, and they need a correct evaluation of their technical, biological, and clinical properties. The present study proposes a new approach for the manufacturing process. We emphasize the key role of each step for combined process of heating, casting and spin for completing works of Ni-Cr alloys with improved physical-chemical properties, as a protocol for quality of the obtained physiognomic dental restorations. The differences in composition distribution between cast and raw materials were investigated by energy dispersive x-ray spectroscopy (EDX), while the surface morphology was inspected by scanning electron microscopy (SEM). Important aspects related to crystal lattice were revealed through the x-ray diffraction (XRD) method and they are closely related to the centrifugal casting process.     

PROM器件中Ni-Cr熔丝的设计

介绍了应用在PROM器件中的Ni-Cr熔丝电阻的设计.熔丝是决定PROM器件稳定性的关键元件.Ni-Cr薄膜材料有良好的半导体加工特性和温度稳定性.通过热学分析和测试实验，得到相关数据,设计出熔丝形状以及三维尺寸.再根据此集成电路器件的整体版图布局设计出可应用到PROM中的Ni-Cr熔丝.采用磁控溅射方法，通过控制工艺条件得到所需的薄膜厚度，经光刻形成所需图形.通过产品的读取测试实验，取得了良好的效果.     

Ni-Cr钢中P的非平衡晶界偏聚现象

采用Auger电子能谱仪分析了经过1000℃淬火后600℃时效过程的Ni-Cr钢中元素磷的晶界偏聚浓度,得到晶界P的偏聚浓度随时效时间变化的动力学曲线。结果表明,Ni-Cr钢在600℃时效60 min时,P的晶界偏聚浓度出现极大峰值,与平衡晶界偏聚模型不符。利用溶质的非平衡晶界偏聚模型进行分析,证实这是由于钢中P的非平衡偏聚临界时间现象引起的。     

铁基镍铬合金膜电解工艺的研究

在盐酸体系中采用膜电解电溶法处理含镍、铬的铁基高温合金。通过优化条件, 确定了膜电解过程的操作条件。研究结果表明, 在电压为1.5 V、平均电流密度为500 A/m²、Ni²⁺离子浓度为1 mol/L、阳极液酸度为1 mol/L、极距为20 mm、温度为35 ℃条件下电解, 电流效率可达90%以上, 能耗为1 200 kW·h/t左右。     

铬颗粒尺寸对镍-铬复合镀层900℃抗空气氧化和耐Na_2SO_4熔盐腐蚀性能的影响

采用复合电镀技术,在镍基体上分别制备了纳米铬-镍复合镀层和微米铬-镍复合镀层,用XRD、SEM/EDS等仪器分别对两种复合镀层在900℃空气中的氧化行为和在900℃Na2SO4熔盐中的热腐蚀行为进行了研究.结果表明:与微米铬粒子增强的Ni-30%Cr复合镀层相比,纳米铬粒子增强的Ni-11%Cr复合镀层表现出更好的抗高温氧化和耐腐蚀性能;铬颗粒尺寸的减小增加了单位面积内Cr2O3的形核量,缩短了不同Cr2O3核间的距离,从而加速了保护性Cr2O3氧化膜的快速形成,这是Ni-11%Cr复合镀层抗氧化和耐腐蚀性能更好的主要原因.     

稀土对高Ni-Cr铸铁石墨的变质作用

采用金相和电镜等手段对稀土在高Ｎｉ－Ｃｒ铸铁中的行为进行了研究。结果表明：稀土可以改善高Ｎｉ－Ｃｒ铸铁石墨的形态及分布，使之由长条状向短厚状过渡。并且随着稀土加入量增多，石墨数量增加。     

镍铬合金激光熔覆层的制备及其表征研究

采用激光熔覆的方法,在45钢表面添加镍包铬复合粉末制得镍铬合金激光熔覆层。结果表明,镍铬合金激光熔覆层主要由Ni、Cr、Fe、C等元素组成,其显微组织是定向凝固的柱状枝晶组织。镍铬合金激光熔覆层熔覆区的平均显微硬度为441.4HV,约为基体45钢显微硬度的1.6倍,熔覆层的磨损量为基体45钢的60%,因此镍铬合金激光熔覆层具有较好的耐磨性能。     

三价铬脉冲电沉积纳米晶Ni-Cr合金工艺

采用脉冲电沉积方法对三价铬电沉积Ni-Cr合金镀层工艺进行研究,确定并优化三价铬脉冲电沉积Ni-Cr合金的最佳镀液配方及工艺参数。研究镀液中各成分及工艺参数对三价铬脉冲电沉积Ni-Cr合金厚度及合金镀层中铬的影响,利用扫描电镜和电子能谱分析Ni-Cr合金镀层的形貌、微观结构和化学组成。结果表明,镀层厚度和Ni-Cr合金中铬含量在不同浓度的络合剂、稳定剂、乙酸钠及不同的电流密度、温度、pH值、占空比和脉冲频率下都存在极大值,且Ni-Cr合金厚度随合金中铬含量的增加而减少。当铬含量为24%时,镀层的厚度大于10μm,无裂纹,其晶粒为纳米球状晶粒。