Nitriding of titanium with plasma jet under reduced pressure

The nitriding of titanium with argon-nitrogen (3%) and argon-nitrogen (3%)-hydrogen (2%) plasma jets at pressures of 190 torr was studied. The reaction kinetics obeyed mainly a parabolic law. The parabolic kinetic constants were 10^–10–10^–8 g² cm^–4 s^–1, which were 2–3 orders of magnitude larger than those in R.F. discharges. From emission spectroscopy, nitrogen atoms in the excited states were observed. The nitrogen atoms can promote the nitriding reaction. The effect of the addition of hydrogen to nitrogen is also briefly discussed.     

不同热处理对热模钢H13的组织和性能的影响

本文研究了热模具钢H13(4Cr_5MoSiV_1)经不同热处理工艺处理后的显微组织和性能。结果表明:H13钢经软氮化处理后,耐磨性、热疲劳抗力较好而冲击韧性较低,250℃等温淬火加回火处理后的冲击韧性最高,热疲劳抗力比正常淬火加回火处理的好,耐磨性较差,300℃等温淬火加回火处理的冲击韧性和热疲劳抗力较低。据此,在受冲击载荷情况下,采用250℃等温淬火加固火热处理工艺较好;受冲击载荷较小时,采用正常淬火加固火软氮化复合热处理工艺较好。     

Monte Carlo simulation of nitriding in iron by a mixing technology with laser and plasma beams

A program is modeled to describe nitriding depth by a new mixing laser and plasma beams nitriding (LPN) technique. The model extends the transport of ions in matter (TRIM) program by adding temperature and energy factors into the energy function. The nitriding depths and nitrogen distribution in substrate were calculated by Monte Carlo program. There is a good agreement between calculation and experiment results at different laser energy intensities, scanning velocities and nitrogen ion energies respectively. Moreover, the nitriding process diagrams by LPN technique are shown from calculation results.     

塑性变形对间隙原子碳、氮、硼扩散速度的影响

本文综合论述了在化学热处理过程中室温形变对间隙原子(C、N、B)扩散速度的影响.认为位错对扩散即有促进作用也有阻碍作用,其主要原因是温度的影响,     

In vitro study of human endothelial progenitor cells behaviour on nitrided Ni-free Ti–27Nb alloy

A superelastic Ni-free Ti–27Nb alloy has been synthesized and gas nitrided at high temperature to investigate its suitability for vascular implant applications. The cellular responses of human endothelial progenitor cells (EPCs) to both bare and nitrided Ti–27Nb alloy have been analyzed using Live/Dead staining, MTT assay, fluorescence microscopy and ELISA technique, as well as NiTi alloy for comparison. Live/Dead staining and MTT assay were performed to assess the cellular viability and proliferation, while fluorescence microscopy was used to analyze cell adhesion, cell morphology, and the expression of endothelial cell markers (VE-cadherin and von Willebrand factor). Secretion of the pro-inflammatory chemokine MCP (monocyte chemoattractant protein)-1 by the cells grown in contact with the analyzed materials was further verified using the enzyme-linked immunosorbent assay. The results obtained revealed that adhesion, spreading, viability, proliferation rate and phenotypic markers expression of EPCs were similar on the surfaces of Ti–27Nb and NiTi alloys. Cells exposed to nitrided Ti–27Nb surface exhibited significantly decreased inflammatory response, which may be beneficial for reducing in-stent restenosis incidence.     

Laser gas-assisted processing of carbon coated and TiC embedded Ti-6Al-4V alloy surface

Laser gas-assisted treatment of Ti-6Al-4V alloy surface is carried out. The alloy surface is initially coated by a carbon layer, in which the TiC particles are embedded prior to laser processing of the surface. The carbon coating with the presence of TiC particles on the workpiece surface is expected to result in carbonitride compound in the surface vicinity after the laser treatment process. Optical and scanning electron microscopes are used to examine the morphological and the metallurgical changes in the laser treated layer. The residual stress formed in the surface region after the laser treatment process is critical for the practical applications of the resulting surface. Therefore, the residual stress formed in the laser treated region is predicted from the analytically equation. The X-ray diffraction technique is incorporated to obtain the residual stress formed in the surface region. It is found that the residual stress predicted agrees with the X-ray diffraction data. The dense structures consisting of TiC_xN_1−x, TiN_x, Ti₂N, and TiC compounds are formed in the surface region of the treated layer. This, in turn, significantly increases the microhardness at the surface.     

Ultrasonic cavitation erosion of gas nitrided Ti–6Al–4V alloys

Ultrasonic cavitation erosion experiments were performed on Ti–6Al–4V alloys samples in annealed, nitrided and nitrided and subsequently heat treated state. The protective oxide layer formed as a result of annealing and heat treatment after nitriding is eliminated after less than 30 min cavitation time, while the nitride layer lasts up to 90 min cavitation time. Once the protective layer is removed, the cavitation process develops by grain boundary erosion, leading to the expulsion of grains from the surface. The gas nitrided Ti–6Al–4V alloy, forming a Ti_xN surface layer, proved to be a better solution to improve the cavitation erosion resistance, compared to the annealed and nitrided and heat treated state, respectively. The analysis of the mean depth of erosion rate at 165 min cavitation time showed an improvement of the cavitation erosion resistance of the nitrided samples of up to 77% higher compared to the one of the annealed samples.     

渗氮/PVDTiN涂层对42CrMo钢组织和性能的影响

采用渗氮+物理沉积TiN涂层的复合表面处理技术,对42CrMo钢进行表面强化处理。通过对复合表面处理后的42CrMo钢进行显微组织观察和性能测试,结果表明4,2CrMo钢表层组织和性能分别受渗氮及PVD工艺和渗碳层与涂层界面之间的结合力影响。此外,表层组织硬度呈现明显的梯度结构,外表层TiN涂层硬度最高可达2 200 HV0.1以上,此层深度在1～3μm,而中间渗氮层硬度达756.1HV0.1,深度在10 mm左右。     

Continuous and discontinuous precipitation in Fe-1 at.%Cr-1 at.%Mo alloy upon nitriding; crystal structure and composition of ternary nitrides

The internal nitriding response of a ternary Fe–1 at.%Cr–1 at.%Mo alloy, which serves as a model alloy for many CrMo-based steels, was investigated. The nitrides developing upon nitriding were characterised by X-ray diffraction, scanning electron microscopy, electron probe microanalysis, transmission electron microscopy and atom probe tomography. The developed nitrides were shown to be (metastable) ternary mixed nitrides, which exhibit complex morphological, compositional and structural transformations as a function of nitriding time. Analogous to nitrided binary Fe–Cr and Fe–Mo alloys, in ternary Fe–Cr–Mo alloys initially continuous precipitation of fine, coherent, cubic, NaCl-type nitride platelets, here with the composition (Cr_½,Mo_½)N_¾, occurs, with the broad faces of the platelets parallel to the {1?0?0}_α-Fe lattice planes. These nitrides undergo a discontinuous precipitation reaction upon prolonged nitriding leading to the development of lamellae of a novel, hexagonal CrMoN₂ nitride along {1?1?0}_α-Fe lattice planes, and of spherical cubic, NaCl-type (Cr,Mo)N _x nitride particles within the ferrite lamellae. The observed structural and compositional changes of the ternary nitrides have been attributed to the thermodynamic and kinetic constraints for the internal precipitation of (misfitting) nitrides in the ferrite matrix.     

不同条件对扩镓硅基GaN晶体膜质量影响的XRD分析

采用射频磁控溅射工艺在扩镓硅基上溅射Ga2O3薄膜氮化反应组装GaN晶体膜,并对其生长条件进行研究。用XRD对样品进行了结构分析,测试结果表明：采用此方法得到的预沉积的扩镓硅基生长GaN晶体膜随着扩镓时间和氮化时间的增加,薄膜的晶化程度得到明显提高。