Surface tension of molten Ni-（Cr, Co, W） alloys and segregation of elements

Surface tension of molten Ni-(Cr, Co, W) alloys was measured at the temperature of 1 773-1 873 K in an Ar+3%H2 atmosphere using an improved sessile drop method. The segregation of Cr, Co and W in alloy was calculated and analyzed using Butler's equation. The results show a good agreement between measured and calculated data. The surface tension of molten Ni-(Cr,Co, W) alloys decreases with increasing temperature. In Ni-(Cr, Co, W) alloys, the element with lower surface tension tends to segregate on the surface of molten alloy while that with higher surface tension tends to segregate inside of the molten alloy. The larger the differences in surface tension, atom radius and electron configuration between solvent and solute are, the more significant the segregation is. As a result, Ni segregates onto the surface and Co and W segregate inside the alloys.     

Corrosion behavior of Cr3C2-NiCr vacuum plasma sprayed coatings

The objective of the present work is to determine the influence of the heat treatment on the corrosion resistance of a Cr₃C₂-NiCr coating of 450 μm thickness, deposited by a vacuum plasma spray process (VPS) on a steel substrate. The post-heat treatment of the as-deposited coating was carried out in Ar at 400 °C and 800 °C, respectively. The coatings were characterized by means of an electron probe micro analyzer (EPMA) with wavelength dispersive X-ray spectrometers (WDS). It was found that no significant changes were produced as a consequence of the heat treatment carried out at 400 °C. Therefore, the corrosion experiments were conducted for the substrate, the as-deposited coating and the post-heat treated coating at 800 °C. Potentiodynamic polarization showed that the annealed coating at 800 °C has a better corrosion resistance than the as-deposited coating. The corrosion current density (I_corr) of this coating was approximately 3 and 4 times smaller than that corresponding to the as-deposited coating and steel substrate, respectively. This significant improvement of the corrosion behavior of the post-heat treated coating is mainly due to both the microstructural changes that take place in the coating and the diffusion of Ni into Fe at the coating-substrate interface, which ensures the presence of a metallurgical bond.     

磨粒真空预钎焊金刚石磨轮的研制及其加工性能分析

分别采用Cu-Sn-Ti合金、A合金稀释的Ni-Cr合金对金刚石真空预钎焊处理,将预钎焊磨粒与金属粉末混匀后热压烧结制作节块和磨轮,并进行磨轮对比磨削实验。由抗压强度、冲击韧性实验测试磨粒力学性能,由抗弯强度实验测试节块抗弯强度。由扫描电镜分析磨粒与胎体界面结合效果。结果表明:Cu基预钎焊磨粒预钎焊层分布均匀,力学性能比A-Ni基预钎焊磨粒提高;预钎焊节块抗弯强度高于常规节块;Cu基预钎焊磨粒与胎体结合致密,界面处Ti元素偏聚富集,Fe、Cu元素相互扩散,实现了牢固化学冶金结合;预钎焊磨轮加工性能明显优于常规磨轮,Cu基预钎焊磨轮锋利度比Ni基预钎焊磨轮提高约15%,实现了多层钎焊效果。     

Cr颗粒尺寸对Ni-Cr复合镀层750℃热腐蚀性能影响

采用复合电镀技术,通过向普通电镀溶液中分别加入平均粒度为40 nm和1~5μm的Cr粉的方法在Ni基材上制备了一种金属Ni基纳米Cr粒子弥散的Ni-Cr纳米复合镀层和一种微米Cr粒子弥散的Ni-Cr复合镀层。混合盐(75 wt%Na2SO4+25wt%NaCl)750℃热腐蚀行为结果表明:与微米Cr粒子弥散的Ni-12.4 wt%Cr复合镀层相比,Ni-11wt%Cr纳米复合镀层表现出更好的耐腐蚀性能。SEM/EDAX、XRD和TEM分析表明,在相同的Cr颗粒含量条件下,Cr颗粒尺寸的降低提高了Ni-Cr复合镀层的抗腐蚀性能,这是因为Cr颗粒尺寸的降低和基体Ni晶粒的细化增加了单位面积内的Cr2O3形核率,缩短不同Cr2O3核间的距离,与此同时基体Ni晶粒的细化有利于保护性氧化物形成元素Cr沿晶界向腐蚀前沿的快速扩散,从而加速了保护性Cr2O3膜的快速形成。     

Ni-Cr合金烤瓷界面反应微观机理

对临床失败Ni-Cr合金烤瓷修复体分析,Ni-Cr合金与陶瓷界面平滑,无明显的反应层生成,修复体内存在裂纹和气孔.通过扫描电镜、能谱与X射线衍射仪,对Ni-Cr合金与陶瓷界面反应研究结果表明,Al2O3陶瓷表面富集的氧离子,与合金中的Ni,Cr反应,还原生成Al,并与Ni化合生成AlNi3,而Cr则被氧化后与Sn生成SnCrO的复合氧化物.在Ni-Cr合金烤瓷界面处形成一连续的反应薄层,可显著改善Ni-Cr合金与陶瓷间的界面冶金结合,减少界面缺陷,实现Ni-Cr合金与陶瓷的可靠结合.     

Cyclic oxidation of Ti3Al-based materials

The microstructure variation and oxidation behavior of a hot-rolled and quenched Ti-24Al-11Nb (at%) intermetallic alloy with and without protective Ni-20Cr (at%) coating were studied in the air at a cyclic annealing temperature of 600?°C and 900?°C. The phase transformations monitored up to 120?h of alloy oxidation and oxidation products were examined using different experimental techniques. The oxidation kinetics was determined by recording the mass gain vs. time data and oxidation activation energy was evaluated. It was found that the annealing temperature and deposited coating significantly affect the scale formation and growth. The alloy showed better oxidation resistance at 600?°C, irrespective of the protective coating application. The higher temperature promoted the formation of thicker and multi-layered scale predominantly composed of Nb-doped TiO₂ and Al₂O₃ oxides, which cracked and spalled causing oxidation rate for an order of magnitude higher than that at 600?°C. The presence of AlN decelerated the oxide scale growth, which obeyed a parabolic rate law. It was also noted that a two-phase α₂+β microstructure changed to a greater extent. With increasing temperature, the α₂→β phase transformation occurred more intensive and new α₂′′ and O-Ti₂AlNb phase appeared. The Ni-20Cr coating reduced the oxidation rate at both temperatures and improved the scale-spallation resistance. The compact Cr₂O₃ layer formed on the coated alloy led to the preferential Al₂O₃ formation, increasing its amount in mixture with Nb-enriched TiO₂ oxide. Thin TiN layer detected beneath the oxide scale also supported the formation of slow-growing Al₂O₃, leading to a decrease in the oxidation rate. The external scale suppression contributed to the greater diffusion zone enrichment, resulting in the faster O-Ti₂AlNb formation. The experimentally observed O-Ti₂AlNb formation was confirmed by ab initio modeling. Furthermore, additional structures were predicted and studied using first-principles calculations in the O-Ti₂AlNb compound.     

固体润滑剂在Ni-Cr合金／Si3N4摩擦副界面的转移行为与摩擦学研究

考察了Ni-Cr-CaF2，Ni-Cr-PbO合金分别与Si3N4配副下的摩擦学性能，运用扫描电镜分析了固体润滑剂在Ni-Cr合金／Si3N4摩擦副界面的转移行为。结果表明，转移膜中CaF2的存在有利于在Si3N4陶瓷上形成有效的转移膜，但是CaF2未在摩擦界面优先转移，而软金属Pb与Si3N4陶瓷的润湿较差，不能存Si3N4陶瓷上形成软金属Pb的完整转移膜。     

光谱辐射测量金属薄膜桥电爆炸温度

采用光谱辐射法测量了Ni-Cr金属薄膜桥的电爆炸温度。通过六通道瞬态光学高温计测量金属薄膜桥电爆炸时在514nm、631nm、692nm、715nm、910nm、1068nm波长处的辐照强度,根据黑体辐射理论计算温度值。研究表明,金属薄膜桥在50V、100μF条件下电爆炸时的最高温度在5000K左右,4000K以上持续时间为300ns。     

Ni-Cr合金烤瓷材料界面组织结构和力学性能

应用扫描电镜、能谱、X射线衍射及电子拉伸试验机对Ni-Cr合金与烤瓷材料的界面组织结构与力学性能进行了分析。结果表明:Ni-Cr合金烤瓷制作过程中产生残余应力和缺陷将导致瓷崩、瓷裂、剥离或脱落。烤瓷温度T对金-瓷界面剪切结合强度影响较大,T=990℃、保温时间t=1.0 min时,金-瓷界面剪切结合强度可达到37.52 MPa。在金-瓷界面处由于Ni-Cr合金与熔融的玻璃相烤瓷材料相互作用,形成新的化合物型界面,对提高金-瓷界面结合强度将起到非常重要的作用。     

陶瓷基体表面粗糙度对Ni-Cr薄膜换能元性能的影响

研究了Al2O3(95%)陶瓷基底的粗糙度对Ni-Cr(80/20)合金薄膜及薄膜换能元性能的影响.利用磁控溅射法在不同粗糙度的基底上制备了Ni-Cr合金薄膜.通过扫描电镜、划痕法、4探针法对薄膜的微观结构、附着性能、电性能进行了研究.根据D-最优化法测定了基底粗糙度不同的薄膜换能元爆发电压、爆发电流.结果表明:随着基...