Microstructure and mechanical properties of an in situ synthesized TiB and TiC reinforced titanium matrix composite coating

A titanium-based composite coating reinforced by in situ synthesized TiB and TiC particles was fabricated on Ti6Al4V by laser cladding. The microstructure and mechanical properties were investigated. The coating was mainly composed of β-Ti cellular dendrites and an eutectic in which a large number of rod/needle-shaped TiB and a few equiaxial TiC particles were homogeneously embedded. The microstructural evolution could be divided into four stages: precipitation and growth of primary β-Ti phase, formation of the binary eutectic β-Ti+TiB, formation of the ternary eutectic β-Ti+TiB+TiC, and solid transformation from β-Ti to β-Ti. Microhardness of the coating showed a gradient variation from the surface (about HV0.2 876) to the bottom (about HV0.2 660) and was prominently improved in comparison with that of the substrate. Fracture toughness of the coating also exhibited a gradient variation from the surface (6.3 MPa·m1/2) to the interface (11.9 MPa·m1/2). Wear resistance of the coating was significantly superior to that of Ti6Al4V.     

Synthesis of Ti3SiC2/TiB2 Composite by In-situ Hot Pressing (HP) Method

Ti3SiC2/TiB2 composite was successfully obtained by hot pressing Ti/TiC/Si/B4C power mixtures.Volume fraction of TiB2 in Ti3SiC2/TiB2 composite can not exceed 10%.Incorporation of excessive TiB2 will affect the reactions process.TiC and Ti5Si3 were two important intermediate phases during the whole reactions.The microstructure characteristics of the Ti3SiC2/TiB2 composites were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The experimental results show that the grains of Ti3SiC2/TiB2 composite are structured in a layered form,and the formation of TiB2 particles as reinforcements with elongated or equiaxed shape distributes in Ti3SiC2 matrix.     

激光熔覆钛基复合涂层的显微组织和硬度分析

采用激光熔覆快速非平衡合成方法制备了原位反应合成TiB增强钛基复合材料.用Y2O3、Ti和B的混合粉末在Ti-6Al-4V基体表面激光熔覆制得TiB/Ti复合涂层.采用X线衍射仪(XRD)、扫描电子显微镜(SEM)、能量散射光谱仪(EDS)和硬度测试等方法,研究了原位合成TiB/Ti复合涂层的显微结构和显微硬度.结果显示:激光熔覆层的相结构主要为α-Ti和TiB两相,TiB增强相均匀地分布于复合涂层中,熔覆层的硬度值高于基体Ti合金的硬度值1倍以上,Y2O3含量(质量分数w,全文同)为1％的激光熔覆涂层内部的增强相组织最为均匀、细小,且硬度值也最高,平均硬度(HV)值约为830.     

Preparation of porous silicon carbide by combustion synthesis

Porous silicon carbide ceramics were prepared by combustion synthesis technique. SiC/TiC composite was gained by combustion reaction of Si, C and Ti. Thermodynamics analysis of Si-C-Ti system indicates that the content of TiC in products should be larger than 30%. The experimental results show that the content of Ti C should be larger than 25% to achieve a complete combustion reaction. The X-ray diffractometry results show that the final products with a relative density of 45%-64% are composed of a-SiC,β-SiC, TiC and a small quantity of Si. The images of scanning electron microscopy show that the structures of grain in SiC based porous ceramics consist of particles with a few microns in size.     

Effect of Y2O3 on cracking susceptibility of laser-clad Ti-based composites coatings

Ti-based composite coatings reinforced by in situ synthesized TiB and TiC were deposited on Ti6AlaV substrates by laser cladding. The effects of Y2O3 on the microstructure and cracking susceptibility of the coatings were investigated in details. It is shown that a small amount of Y2O3 addition can significantly refine the microstructure of the coatings by hastening spheroidization of the primary phase structure. The maximum refinement in microstructure was obtained with the optimum （2 wt%） addition of Y2O3. Moreover, it can increase the volume fraction of TiC and reduce the residual stress of the coatings due to the decrease in lattice distortion of the α（Ti） matrix. All of these factors lead to the reduction in cracking susceptibility of the coatings containing Y2O3 on the premise that the hardness of the coatings is improved. The fracture toughness of the coatings without and with Y2O3 （2 wt%） is 8.32 and 17.36 MPa.m1/2, respectively. Scanning electron microscope examination reveals a transition of the fractured surfaces from cleavage fracture to quasi-cleavage fracture resulting from the Y2O3 addition.     

Microstructure and wear properties of the electroslag remelting layer reinforced by TiC particles

The electroslag remelting (ESR) layer reinforced by TiC particles was obtained by electroslag remelting. The microstruc-ture and wear properties of the ESR layer were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and wear test. The results indicate that TiC particles are synthesized by self-propagating high-temperature synthesis (SHS) reaction during the electroslag remelting process. The size of TiC particles is in the range of 1-10 μm, and the distribution of TiC particl...     

Precipitation characteristic of high strength steels microalloyed with titanium produced by compact strip production

Transmission electron microscopy (TEM) and physics-chemical phase analysis were employed to investigate the precipitates in high strength steels microalloyed with Ti produced by compact strip production (CSP). It was seen that precipitates in Ti microalloyed steels mainly included TiN, Ti4C2S2, and TiC. The size of TiN particles varied from 50 to 500 nm, and they could precipitate during or before soaking. The Ti4C2S2 with the size of 40-100 nm might precipitate before rolling, and the TiC particles with the size of 5-50 nm precipitated heterogeneously. High Ti content would lead to the presence of bigger TiC particles that precipitated in austenite, and by contrast, TiC particles that precipitated in ferrite and the transformation of austenite to ferrite was smaller. They were less than 30 nm and mainly responsible for precipitate strengthening. It should be noted that the TiC particles in higher Ti content were generally smaller than those in the steel with a lower Ti content.     

原位自生TiC颗粒对铁基耐磨堆焊金属的影响

为了研究原位自生TiC颗粒对堆焊层组织与性能的影响,采用药芯焊丝明弧堆焊方法在Q235钢表面制备了Fe-Cr-Ti-C堆焊合金.利用X射线衍射仪、扫描电子显微镜、洛氏硬度计和湿砂磨损试验机对堆焊合金进行了分析.结果表明,加入的Ti元素可在堆焊层中原位生成TiC硬质相颗粒,并促进M7C3硬质相的生成,从而起到细化晶粒的作用.当生成的TiC和M7C3硬质相数量较多且弥散分布于金属基体中时,这些硬质相可起到相应的抗磨骨架作用,从而提高了堆焊金属的耐磨性.当药芯焊丝中Ti元素的质量分数为7%时,堆焊层性能最佳,其硬度值为61.6HRC,磨损量为0.3904g.     

Combustion Synthesis and Densification of NiAl/TiB_2 Composites

A suitable combustion synthesis and densification process was designed to fabricate dense NiAl/ TiB2 composites from Ni-Al- Ti-B system. Combustion synthesis processing and microstructure characteristics of products were studied in detail. The results show that the amount of TiB2 ceramics has a great influence on the combustion synthesis processing and microstructure; with the increase of the amount of TiB2 ceramics, the combustion temperature and combustion velocity increase rapidly. The volume of synthesized products and the grain size of ceramics particle size are also affected by the amount of TiB2 ceramics. TiB2 ceramics fiber can be produced in this synthesis system. The dense NiAl/ TiB2 composites with residual porosity of no more than 1% are fabricated by the combustion synthesis and hot pressing, the mechanical properties of the dense NiAl/ TiB2 composites increase with increase of the amount of TiB2 ceramics.     

Wear-resistance Performance of Spray-welding Coating by Plasma Weld-surfacing

Alloy powders including Ni60, WC, Cr_3C_2, and TiC with different mass ratios were deposited on medium carbon low alloy steel by plasma welding. Through the experiments, the optimal alloy powder reinforcing cutter tool surface properties were discovered. The wear resistance properties were investigated on the impact abrasive wear tester. The experimental results show that in terms of microstructure, there exists the shape of herringbone, spider mesh, broken flower structures in coatings. In addition, fusion area of four specimens surfacing welding layer displays a large number of acicular martensite with a small amount of austenite. The coating mainly consists of Ni-Cr-Fe austenitic phase and the other precipitates. TiC density is smaller, its content is less in alloy powder, in the process of surfacing welding, TiC is melted fully, which is mainly distributed in surface layer and middle layer of hard facing layer. The content of TiC gradually reduces from surface layer of hard facing layer to the fusion area. Compared to TiC, the density of tungsten carbide and chromium carbide is larger, there exist tungsten carbide and chromium carbide particles, which are not completely melted near the fusion area. The micro-hardness presents gradient change from the fusion area to the surface layer of hard facing layer, and the hardness of the middle layer is slightly lower than that of the fusion area, and the hardness increases near the surface layer.     

Instability of TiC and TiAl3 compounds in Al-10Mg and Al-5Cu alloys by addition of Al-Ti-C master alloy

The performance of Al-Ti-C master alloy in refining Al-10Mg and Al-5Cu alloys was studied by using electron probe micro-analyzer （EPMA） and X-ray diffractometer （XRD） analysis. The results indicate that there are obvious fading phenomena in both Al-10Mg and Al-5Cu alloys with the addition of Al-5Ti-0.4C refiner which contains TiC and TiAl3 compounds. Mg element has no influence on the stability of TiC and TiAl3, while TiC particles in Al-10Mg alloy react with Al to form Al4C3 particles, resulting in the refinement fading. However, TiC particles are relatively stable in Al-5Cu alloy, while TiAl3 phase reacts with Al2Cu to produce a new phase Ti（Al, Cu）2, which is responsible for the refinement fading in Al-5Cu alloy. These indicate that the refinement fading will not occur only when both the TiC particles and TiAl3 compound of Al-Ti-C refiner are stable in Al alloys.     

工艺参数对钎焊TC4接头微观组织及显微硬度的影响

采用Ti-Zr-Cu-Ni非晶钎料真空钎焊TC4钛合金,研究不同保温时间对钎焊接头的影响.采用光学显微镜(OM),扫描电子显微镜(SEM),能谱仪(EDS)和显微硬度计对接头的显微组织和力学性能进行分析.结果 表明,焊缝主要组织为α-Ti与β-Ti,且随着保温时间的增加,焊缝区逐渐增厚,组织逐渐粗大.当保温时间为40 ...     

Effects of Ta addition on the microstructure and mechanical properties of Ti40Zr25Ni8Cu9Be18 amorphous alloy

The effects of Ta addition on the microstructure and mechanical properties of Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ bulk amorphous alloy were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scan electron microscopy (SEM) and compressive testing. As a result, the addition of Ta (0-8at%) prompted the successive precipitation of quasicrystalline phase, CuTi₂ phase and bcc β-Ti solid solution. Additionally, the addition of less Ta content (3at%-5at%) led to the formation of amorphous matrix/nanoquasicrystal/CuTi₂ complex phase structure; and nanoquasicrystals, as reinforcement precipitates, improved the fracture strength of Ti-Zr-Ni-Cu-Be-Ta alloys, which led to the high compressive fracture strength 1856 MPa of Ta5 alloy. With increasing Ta content (5at%-8at%), although the ductile dendritic β-Ti solid solution was precipitated, the strength and plasticity decreased to a great extent resulting from the growth of quasicrystalline phase and CuTi₂ phase.     

机械合金化制备碳化钛纳米粉体的合成机理研究

本研究中,以金属钛（Ti）粉与环己烷为原料,利用机械合金化制备了碳化钛（TiC）纳米粉体。利用X射线衍射并结合Rietveld精修对球磨产物进行定性与定量分析;借助透射电子显微镜对产物进行形貌与元素以及结晶性进行分析;对球磨过程中TiC的合成机理进行了研究。结果表明,球磨产物中主相为TiC,另有少量残留的氢化钛（TiH2）与Ti;所制备TiC粉体易于团聚、颗粒度均匀、结晶性良好;TiC合成机理属于扩散型机制。     

PCVD-TiC膜的工艺及其应用研究

通过正交试验对ＰＣＶＤ－ＴｉＣ膜的镀膜工艺参数进行了优化，得到了制备高硬度、高结合牢度和高沉积速率ＴｉＣ膜的工艺参数。试验表明，在用ＰＣＶＤ法沉积ＴｉＣ膜的过程中，ＴｉＣｌ４和ＣＨ４的流量是重要的控制参数。过多的ＴｉＣｌ４和ＣＨ４都会给ＴｉＣ膜带来不利的影响。氩气虽然可以提高ＴｉＣ膜的沉积速率，但同时也降低了膜与基之间的结合牢度。在冷挤压模具上应用的结果表明，镀有优化后的ＰＣＶＤ－ＴｉＣ膜的模具比镀ＴｉＮ膜的模具可提高寿命２～４倍。与不镀膜的模具相比，可提高寿命１０倍以上。     

Self-Propagating High-Temperature Reductive Synthesis of TiB_2-Al_2O_3 Composite Powders

TiB2-Al2O3 composite powders were produced by self-propagating high-temperature synthesis(SHS) method with reductive process from B2O3-TiO2-Al system. X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses show the presence of TiB2 and Al2O3 only in the composite powders produced by SHS. The powders are uniform and free-agglomerate. Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) observation of microstructure of the composite powders indicate that the interfaces of the TiB2-Al2O3 bond well, without any interfacial reaction products. It is proposed that the good interfacial bonding of the composite powders can be resulted from the TiB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.     

Si3N4/TiC纳米复合陶瓷材料显微结构

利用日立H-800透射电境、日立S-570型扫描电境及RAX-10A型X射线衍射仪对Si3N4/TiC纳米复合陶瓷材料的微观组织、结构和成分进行了研究.结果表明,TiC纳米颗粒弥散分布在基体β-Si3N4晶内和晶界,所制备的材料为晶内/晶间混合型纳米复合陶瓷.通过对Si3N4/TiC纳米复合陶瓷材料断裂方式的观察表明,材料断裂为沿晶断裂和穿晶断裂复合型,纳米粒子对裂纹扩展起到偏转和钉扎作用.纳米Si3N4颗粒的加入促进了基体长柱状β-Si3N4晶粒多峰分布的形成,类晶须晶粒在裂纹扩展过程中产生桥接和拔出.     

Diffusion reaction in the interface of titanium/mild steel composite

The microstructure together with the formation and growth of reaction phases in the interfacial diffusion zone of the explosive cladding TA2/A3 has been investigated by means of OM, SEM, AES and XRD techniques. When the specimen annealed at temperature under theβ-Ti→α-Ti transformation, i. e. below 1 173 K, only TiC forms along TA2 side of interface and hinders the interdiffusion of Fe and Ti atoms, thus Fe₂Ti or FeTi is unable to occur. While heated up to the transformation temperature ofβ-Ti, e. g, over 1 223 K, the parabolic growth of intermetallic compounds of Fe₂Ti and FeTi with layer structure may form intergranularly and the formation ofβ-Ti orβ-Ti+α-Ti structure at the Fe enriched side of TA2 and the martensitic transformation products at the Fe-depleted side are observed owing to the diffusion of Fe. Furthermore, the growth ofβ-Ti transformation layer is revealed to follow the parabolic rule. Project supported by the Non-ferrous Metal Industry Corperation of China Synopsis of the first author Yang Yang, professor, Dr.-Ing., born on Nov. 11, 1963, has published more than twenty papers. Study fields are on the metallurgical effects of shock deformation on metals, interface of composite, roll and explosive cladding technologies, etc.     

TiC陶瓷滤片的制备及其性能研究

在对TiC陶瓷的性能及其制备工艺进行分析研究的基础上,利用SHS/PHIP技术制备了致密的TiC-TiB2复相陶瓷材料,并对材料进行切割加工成型和清洗,得到和所需滤片形状相同的TiC-TiB2复相陶瓷片,然后再根据TiC和TiB2化学性能的差异,用王水的强腐蚀性溶解其中的TiB2陶瓷相从而得到孔隙大小均匀的、性能优异的TiC陶瓷滤片.用该方法制备的TiC陶瓷滤片,孔隙的直径范围在2~3μm,分布均匀,可以在任何性质的液体中使用,也可用于熔融金属液的过滤.     

Microstructure and tribological properties of laser clad Ni-Ag/Tic composite coating

Ni-Ag/TiC composite coating was prepared on the 45 steel substrates by means of laser cladding. Microstructure and wear properties of composite coatings were analyzed using optical microscopy, field emission scanning electron microscopy and wear machine. The experimental results show that defects, such as cracks and pores, do not occur in the laser-cladded Ni-Ag/TiC composite coating and 45 steel substrate, and they present good metallurgical bonding between them. Compared with Ni/TiC composite coating, micro- hardness values of the two coatings do not present evident differences. The wear experiment result shows that Ni-Ag/TiC composite coated with Ag possesses low friction coefficient and good wear resistance compared with Ni/TiC composite coating.