Microstructures and properties of nickel-titanium carbide composites fabricated by laser cladding

In this work, Ni/TiC composites were synthesized by the laser cladding technique (LCT). A scanning electron microscope (SEM), X-ray diffractometer (XRD), microhardness meter, electrochemical workstation, and friction and wear tester examined the microstructure, surface morphology, phase structure, microhardness, wear, and corrosion resistances of the Ni/TiC composites. These results indicated the Ni/40TiC composite contained finer equiaxed crystals than the Ni and Ni/20TiC composites. In addition, numerous TiC particles in the Ni/40TiC composite impeded growth of the nickel crystals, which resulted in the fine microstructure of the Ni/40TiC composite. The Ni, Ni/20TiC, and Ni/40TiC composites exhibited face-centered cubic (f c c) lattices. The average microhardness values of the Ni/20TiC and Ni/40TiC composites were approximately 748 HV and 851 HV, respectively. The Ni/40TiC composite had the lowest friction coefficient (0.43) among all three coatings, and only some shallow scratches appeared on the surface of the Ni/40TiC composite. The corrosion potential (E) of Ni/40TiC exceeded the Ni/20TiC composite, and both were larger than the Ni composite, which indicated the Ni/40TiC composite had outstanding corrosion resistance and the Ni composite had poor corrosion resistance. The corrosion current densities (i) of Ni, Ni/20TiC, and Ni/40TiC composites were 5.912, 4.405, and 3.248 μA/cm², respectively.     

Optimized microwave absorption properties by tailoring the morphology of carbon coated TiC nanoparticles by N2 pressure

Increasing the dielectric loss capacity plays an important role in enhancing the electromagnetic absorption performance of materials. It remains a challenge to simultaneously introduce multiple types of dielectric losses in the material. In this work, we show that the atomic and interfacial dipole polarizations can be simultaneously enhanced by substituting N species into both carbon coating layers and bulk TiC lattices of a core-shell TiC@C material. Additionally, substitution of N species results more exposed TiC(111) facets and refines the TiC grain sizes in the bulk material, which is beneficial for enhancing the scattering of the external electromagnetic waves. The maximum reflection loss of the N substituted TiC@C material is measured as ?47.1 dB with an effective absorbing bandwidth of 4.83 GHz at 1.9 mm, which illustrates a valuable way to further tuning the electromagnetic absorption performance of this type of materials.     

Electrical performance of fine-grained Y-TZP/TiC composites obtained through a hydrothermal-assisted sol-gel process

Y₂O₃-stabilized tetragonal ZrO₂ polycrystal (Y-TZP) composites with various TiC contents were successfully synthesized via a modified hydrothermal-assisted sol-gel method. Fine precursor powders can be obtained with high crystallinity, nanoscale grain size and uniform morphology. SEM images of the ceramic products show that TiC particles are distributed homogeneously in the final Y-TZP matrix, and their average grain sizes are approximately 390–670 nm and 150–230 nm for the Y-TZP and TiC phases, respectively. A higher TiC volume fraction has a negative effect on the relative density and hardness but a significant positive influence on electrical conductivity. The electrical conductivity values are increased from 115 S/m to 1.23 × 10⁵ S/m with TiC contents varying, demonstrating that the percolation threshold is approximately as low as 11.6 vol% for the samples, which is much lower than those of previous Y-TZP/TiC ceramics. The high electrical performance is probably due to the high D (the diameters of the insulating particles)/d (the diameters of conductive particles) ratio and submicron-sized grains.     

Formation and growth mechanism of TiC crystal in TiC_p/Ti composites

1　ＩＮＴＲＯＤＵＣＴＩＯＮＰａｒｔｉｃｌｅｓｒｅｉｎｆｏｒｃｅｄｔｉｔａｎｉｕｍａｌｌｏｙｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓ(ＴＭＣｐ)ｈａｖｅｗｉｄｅａｐｐｌｉｃａｔｉｏｎｆｉｅｌｄｓｆｏｒｔｈｅｉｒａｔｔｒａｃｔｉｖｅｈｉｇｈｓｐｅｃｉｆｉｃｓｔｒｅｎｇ     

钛化物在铝熔体中的沉淀现象

为了研究导致细化衰退的钛化物沉淀现象，以中间合金为细化剂对工业纯铝进行了细化处理，得到了不同沉淀时间的沉淀试样，利用金相、SEM等技术分析了试样底部沉淀物的显微组织．结果表明：加入中间合金后，试样均存在明显的软化物沉淀现象，且沉淀物中既有TiC(TiB2)化合物，也有TiAl3化合物；沉淀物中的TiAl3与原中间合金中的TiAl3形态一致，说明原中间合金中的一些TiAl3化合物在没有分解完全时就已沉到试样底部；AlTiC中间合金比AlTiB中间合金的钛化物沉淀倾向明显．     

颗粒类型对颗粒增强铝基复合材料性能的影响

本文对粉末冶金法制备的ＳｉＣ和ＴｉＣ颗粒增强铝基复合材料进行了研究。试验表明，在颗粒含量相同、尺寸相当的条件下，ＴｉＣ增强Ａｌ基复合材料的强度和模量均低于ＳｉＣ增强Ａｌ基复合材料，但其屈强比却明显高于ＳｉＣ增强Ａｌ基复合材料。高温长时间等温处理对ＴｉＣ颗粒增强纯Ａｌ复合材料的强度没有明显的影响。     

Strengths and ductility of Mo–TiC alloys after secondary recrystallization

A series of Mo–TiC alloys were heated in vacuum at 2473 K for 36 ks. First grain growth behavior was observed using a scanning electron microscope. Then effects of TiC addition on the strengths and ductility at low temperature were discussed from the viewpoints of chemical composition and grain structure.

Materials with TiC additions of not larger than 0.1% demonstrated a single-crystalline grain structure. Both yield and maximum strengths increased by TiC addition and consequently ductility was improved.     

TiC及Ti2C在铝结晶过程中的核心作用

将工业纯铝（９９．７％）用亚包晶成分的Ｔｉ（＜０．１５％）实行变质处理，采用电子衍射等方法研究其结晶核心，证明α－Ａｌ核心除ＴｉＣ粒子外，还存在Ｔｉ_２Ｃ。ＴｉＣ为立方晶格，ａ＝０．４３８０ｎｍ；Ｔｉ_２Ｃ为正交晶格，ａ＝１．２０ｎｍ，ｂ＝１．０６ｎｍ，ｃ＝１．５０ｎｍ     

钢表面化学气相沉积TiC晶体的择优取向

本文用化学气相沉积(CVD)法,以TiCl_4-CH_4-H_2为原料气体,在不锈钢表面获得了致密的TiC膜.研究了TiC的成膜速度、表面形貌和晶体择优取向与沉积条什的关系.结果表明,沉积温度T_(dep),碳钛比CH_4/TiCl_4强烈地影响了TiC的成膜速度、表面形貌和晶体择优取向.CH_4/TiCl_4低时,TiC晶体的择优取向为(220):而CH_4/TiCl_4高时,TiC晶体的择优取向为(200).TiC晶体的择优取向主要取决于气氛中活性碳的平衡浓度。     

Synthesis of TiC by Self-propagating High-temperature Synthesis with Reduction Stage

Fine powder of TiC was prepared by self-propagating high-temperature synthesis(SHS)method with re-duction stage.The influence of diluent and relative density of the sample on both combustion rate and combus-tion temperature has been studied.The combustion reaction in the system of TiO_2-Mg-C begins at the meltingof Mg.The propagation of combustion wave is related to the gasifying of Mg.The activation energy of theprocess has an approximate linear dependence on the porosity of the sample.