Effect of Surface Treatment on Elemental Composition of Recast NiCr Alloy

Objective: The aim of this study was to compare the effects of different surface treatments on the elemental composition stability of as-received and recast types of NiCr casting alloys. Material and Methods: Six commercial NiCr dental casting alloys (Kera N, Nodelco, Bellabond, Wiron 99, Metaplus VK, and Tritech D) were used in this study. Seventy-two specimens (12 × 12 × 1.2 mm) were produced using the lost-wax casting process. Three casting protocols were established in relation to the proportion of as-received and recast alloys: Group A (100% as-received metal), Group B (50 wt% new metal, 50 wt% once-recast metal), and Group C (100% once-recast metal). Two specimens in every group received two different surface treatments: sandblasting with 110 μmm Al2O3 or oxidation firing. An elemental analysis was performed with x-ray energy-dispersive spectroscopy. Results were subjected to one-way analysis of variance and Tukey HSD tests. Results: The elemental composition was significantly different in the casting groups and treatment groups (p < 0.05). The lowest mean weight percentage Ni value was recorded for Group C and the highest for Group A. Aluminum-oxide sandblasting of the alloy surface reduced the mean weight percentage for Cr. Conclusion: Recasting metal alloys may adversely affect surface quality.

Effect of Rare Earth Elements on Carbide Morphology and Phase Transformation Dynamics of High Ni-Cr Alloy Cast Iron

The effect of rare earth(RE) elements on carbide of high NiCr alloy cast iron was investigated. Meanwhile, the continuous cooling transformation(CCT) curves of cast iron with and without RE addition were determined. The results show that the carbides in high NiCr cast iron can be refined and changed from network and long strip structures into island and block ones. The phase transformation temperature was raised and incubation period of bainite transformation was shortened by adding RE element in high NiCr alloy cast iron.

Surface and Electrical Properties of NiCr Thin Films Prepared by DC Magnetron Sputtering

Several batches of NiCr alloy thin films with different thickness were prepared in a multi-targets magnetron sputtering apparatus by changing sputtering time while keeping sputtering target power of Ni and Cr fixed. Then the as-deposited films were characterized by energy-dispersive X-Ray spectrometer （EDX）, Atomic Force Microscope （AFM） and four-point probe （FPP） to measure surface grain size, roughness and sheet resistance. The film thickness was measured by Alpha-Step IQ Profilers. The thickness dependence of surface roughness, lateral grain size and resistivity was also studied. The experimental results show that the grain size increases with film thickness and the surface roughness reaches the order of nanometer at all film thickness. The as-deposited film resistivity decreases with film thickness.

Heterostructured NiCr matrix composites with high strength and wear resistance

Self-lubricating composites are required to have excellent tribological performances and good mechanical properties when they are applied as mechanic parts.However,the brittle nature of most lubricants will weaken the mechanical properties of the composites where in order to get the lubricating ability proper amount of lubricants are usually incorporated,bringing challenges for them to get well-balanced mechanical and tribological properties.In this study,Ni Cr matrix self-lubricating composites with the addition of WS_(2)and nano-Ti were prepared via spark plasma sintering.The hard phase of Ni_(3)Ti and the lubricant Ti S were formed via in-situ reaction at the interface,which surrounded the soft alloy matrix and developed a heterostructure.Compared with the conventional Ni Cr-WS_(2)composite,the heterostructured composite exhibited a high yield strength of 1645 MPa,a low friction coefficient of 0.37 and a wear rate of as low as 2.25×10^(-5)mm^(3)N^(-1)m^(-1)when sliding.Finite element analysis demonstrated that the heterostructure plays a key role to balance well the mechanical and tribological properties of the Ni Cr matrix composites.

Wear Behavior of a NiCr/AgVO_3 Self-Lubricating Composite

NiCr/AgVO3 self-lubricating composite was prepared by powder cold-pressed method with the NiCr alloy as the matrix and 10 wt.% additive of AgVO3 as solid lubricant. The AgVO3 additive powder was synthesized by the precipitation method which exhibits a melting point of 460℃. Microstructure, phase composition and thermal properties of the AgVO3 powder, as well as the composite of NiCr/AgVO3 were analyzed using scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and differential scanning calorimeter （DSC）. The friction and wear behavior of the specimens from room temperature （R.T.） to 800℃ was evaluated using a ball-on-disk tribometer and 3D white light interference （WLI）. The results showed that the friction coefficient of this material under atmosphere decreases with temperature increasing from R.T. to 800 ~C. However, the wear rate firstly increases from R.T. to 200℃, almost remains stable from 200℃ to 600℃, and then decreases with further increasing the temperature up to 800 ℃. It is also found that the prepared composite materials show a better frictional behavior than NiCr alloy over the whole range of temperatures, which is mainly attributed to solid lubrication of AgVO3 exhibiting a lamella-slip structure at temperatures below 460℃ and forms liquid-film at elevated temperatures above the melting point.