Effect of Cr Content on the Compression Properties and Abrasive Wear Behavior of the High-Volume Fraction(TiC–TiB_2)/Cu Composites

The(TiC–TiB2)/Cu composites with 50 vol% Ti C–Ti B2 ceramic particles were successfully fabricated by the combustion synthesis and hot press consolidation in a Cu–Ti–B4C–Cr system. The effects of the Cr content on the microstructures, hardness, compression properties, and abrasive wear behaviors of the composites were investigated. The final products consist of only Cu, Ti C, and Ti B2 phases, and the ceramic particles are distributed uniformly in these composites. The size of the ceramic particles decreases with Cr addition. As the Cr content increases, the yield strength,ultimate compression strength, microhardness, and abrasive wear resistance of the composites increase, and the fracture strain decreases.     

High-temperature compressive properties of TiC–TiB_2/Cu composites prepared by self-propagating high-temperature synthesis

TiC–TiB2 /Cu composites were prepared by self-propagating high-temperature synthesis with pseudo hot isostatic pressing using Ti, B4 C, and Cu powders. The compressive deformation of the composites at high temperature was investigated. It is found that the maximum compressive strength decreases with the increase of temperature and Cu content. The deformation of the composites includes the steps of elastic, stable rheology, and inaction. The maximum strain is in the range of 5 %–10 %. Before fracture, TiC–TiB2 /40Cu becomes drum-shaped at 1123 K; however, TiC–TiB2 /20Cu only has a brittle fracture along the axial direction of 45°. The results show that the compressive strength of TiC–TiB2 /Cu decreases from 823 to 1223 K. However, the maximum compressive strength of TiC–TiB2 /20Cu reaches 1850 MPa at 823 K, which predicts that this series of composites could be applied to high-temperature compressive materials.     

Microstructure and formation mechanism of in-situ TiC-TiB2/Fe composite coating

Steel matrix composite coatings locally reinforced with in situ TiC-TiB2 particulates were prepared by argon arc cladding（AAC） with different mass fractions of Fe and Ti＋B4C powders as the binding materials. The microstructure, micro-hardness and wear resistance were investigated using SEM, XRD, Micro-hardness Tester, and Friction and Wear Tester, respectively. The results show that the main phases of coating are TiC, TiB2 and a-Fe. The excellent metallurgical bonding is formed between the composite coating and substrate. The coating is uniform, continuous and almost defect-free and the particles are dispersively distributed in the cladded coating. Moreover, the formation mechanism was investigated. With the increase of the content of TiC＋TiB2, the micro-hardness and wear resistance are also improved at the room temperature under normal atmosphere conditions.     

Microstructure and melting properties of Ag–Cu–In intermediate-temperature brazing alloys

The microstructure and melting properties of ternary Ag–Cu–In intermediate-temperature alloys(400–600 °C) prepared by electric arc melting were investigated in this work. The melting properties, phase compositions, microstructure and hardness were characterized by differential scanning calorimetry(DSC), X-ray diffraction(XRD), scanning electron microscopy(SEM)and micro-hardness tester, respectively. The results show that the melting properties, phase compositions, microstructure and hardness of Ag–Cu–In brazing alloys are substantially different when adding different levels of indium. Indium element could effectively reduce the melting temperatures of(Ag–Cu28)–x In alloys, and the melting temperatures of(Ag–Cu28)–25In alloy are located at 497.86 and 617.48 °C. When the indium content varies from 5 wt% and 10 wt%, the dominant phases in the alloys are Ag-rich and Cu-rich phases, and their granular crystals are smaller than 0.5 lm. When the indium content is higher than 15 wt%, the phase compositions of the alloy are Ag4 In and Cu11In9, and the microstructure exhibits dendritic crystals with a uniform distribution. The hardness of(Ag–Cu28)–x In alloy decreases first and then increases with the content of indium increasing, and the highest hardness of(Ag–Cu28)–25In alloy is HV 266.0.     

Enhanced mechanical properties in Al/diamond composites by Si addition

Diamond particles reinforced aluminum–silicon matrix composites,abbreviated as Al(Si)/diamond composites,were fabricated by squeeze casting.The effect of Si content on the microstructure and mechanical properties of the composites were investigated.The mechanical properties are found to increase monotonically with Si content increasing up to 7.0 wt%.The Al-7.0 wt% Si/diamond composite exhibits tensile strength of 78 MPa,bending strength of 230 MPa,and compressive strength of426 MPa.Al–Si eutectic phases are shown to connect with Al matrix and diamond particles tightly,which is responsible for the enhancement of mechanical properties in the Al(Si)/diamond composites.     

Selective Laser Melting of In Situ TiB/Ti6Al4V Composites: Formability,Microstructure Evolution and Mechanical Performance

In the present study, a series of in situ TiB/Ti6Al4V composites were fabricated using selective laser melting. The formability, microstructure evolution and mechanical properties of the as-built samples added with different contents of TiB_2 were studied. It is found that the densification level is related to both the content of TiB_2 and laser energy density. The added TiB_2 reinforcement particle can spontaneously react with titanium and then form the TiB phase. The needle-like TiB phase tends to transform into dot-like particles with the decrease in energy density. Additionally, with the increase in TiB_2 content, the TiB phase is coarsened due to the increased nucleation rate and more reactions. The grain morphology is found to largely depend on the translational speed of solid–fluid interface determined by the temperature gradient and cooling rate. Also, the microhardness of the as-built TiB/Ti6Al4V composites is obviously improved. More interestingly, as the energy density increases, the microhardness of the as-built TiB/Ti6Al4V composites firstly increases and then decreases due to the synergy of grain size and different morphologies and distribution of TiB phases. The wear resistance of TiB/Ti6Al4V composites is far superior to that of Ti6Al4V alloy owing to the increased microhardness resulted from the uniform distribution of the hard TiB phase in the matrix.     

Effect of cenospheres addition on microstructure and properties of AZ91D alloy

The cenospheres/AZ91D composites were fabricated by melt stir method. The phases, microstructure and tensile fracture morphology of the composites were analyzed using XRD, Olympus metallurgical microscopy and SEM methods. The thermal expansion coefficient(CTE) and tensile properties were measured. The results showed that the cenospheres distribute uniformly in the Mg alloy matrix and refine the matrix microstructure. Mg2 Si and MgO were found in addition to α-Mg and β-Mg17Al12 phases using XRD. The CTE of the composites reduced after the cenospheres are added. The yield strength of the composites increases significantly with an increase in the mass fraction and a decrease in the size of the cenospheres. The tensile strength of the composites achieves maximum when the mass fraction of cenospheres is 9wt.% and the size of cenospheres is 80 μm. The fracture mechanism of the composites is cleavage fracture.     

Effect of carbon content on microstructure and property of TiC/Ti-6Al-4V composites

TiC reinforced Ti-6Al-4V matrix composites were fabricated by consumable arc-melting technology utilizing the reaction between titanium and graphite. The phase composition, microstructure and hardness of the TiC/Ti-6Al-4V composites were investigated by XRD, SEM and hardness testing equipment, respectively. The results show that the reinforcements are distributed uniformly in the matrix alloy. With the carbon content of the composites increasing from 0.15% to2.0%, the morphology of TiC transforms from particle into short-bar shape or chain-type consisting of featheriness or wheat-shape and finally into dendritic. Simultaneously, the hardness of the composites increases. The formation mechanisms of TiC can be analyzed as follows： the growth of dendritic primary TiC before the peritectic reaction is dominated by the solute concentration gradient, after peritectic reaction, the nucleation and growth of TiC in β-Ti leads to its forming of short-bar shape. The dendritic TiC mainly is distributed in the matrix grain, but the short-bar shape TiC mainly segregates at the grain boundary, especially at the triangular grain boundaries.     

Microstructure and phase compositions of as-cast Mg–3.9Zn–0.6RE(Gd,Y) alloy with different Gd/Y ratios

Mg–Zn–RE(Gd, Y) alloys with different Gd/Y atomic ratios were prepared by conventional casting, and the microstructure of the alloys was studied by multiple means. Icosahedral quasicrystal phases are observed in all alloys. The different Gd/Y atomic ratios affect the microstructures of the alloys irregularly. The alloy with more Gd has large dendritic structure and more complicated phase composition which are composed of I-phase lamellar eutectic, W-phase divorced eutectic, Mg–RE cuboid particles and Mg–Zn binary phases. Other two alloys show similar microstructures and phase compositions with very thin lamellar eutectics which distribute along the interdendritic region, and the lamellar eutectics are formed by I-phase and Mg. The element contents of the I-phases and Mg–RE phases are partially controlled by the Gd/Y atomic ratio.     

Interfacial microstructure of 20% SO2/Al matrix composites reinforced with in situ formation ceramic phases

Al matrix composites reinforced with in situ ceramic phases by adding 20% SiO2 were fabricated by powder metallurgy process.The interfacial microstructure of the composites was studied by means of SEM and HREM.It was shown that the ceramic phases mainly composed of spinel MgAl2O4 are formed in situ in the original SiO2 particle and the size of small MgAl2O4 crystallites is about dozens of nanometers,which can adjacent to Al and Si.MgO could not found in original SiO2 particle but a little in matrix and may exist with Si,Mg2Si and Al.Si is mostly distributed in matrix and forms some segregation zones.The size of Mg2Si is about 50-100nm and can usually be seen in the matrix.     

立方氮化硼用量及粒度对其同钛铝碳结合剂的反应程度的影响

为研究CBN用量对Ti₃AlC₂结合剂CBN复合材料的影响,使用不同质量配比的Ti3AlC2粉体和CBN粉体通过放电等离子体烧结的方式制备试样,并对比其物相组成和显微形貌。结果表明:当CBN质量分数为10%时,试样的主相为Ti₃AlC₂、CBN和TiC;当CBN质量分数为20%~40%时,生成了TiC、TiN、AlN、TiB₂等物相。另一方面,当CBN质量分数为10%和20%时,CBN表面会形成厚约10 μm的过渡层;当CBN质量分数为30%和40%时,CBN与基体间没有过渡层。若选用粒度尺寸为10 μm的CBN（质量分数为10%）进行烧结,则复合材料中出现许多气孔,基体主相为TiC等轴晶粒且在CBN表面形成厚度1~2 μm的过渡层。CBN质量分数越大或粒度尺寸越小,其同Ti₃AlC₂的反应越充分、过渡层越薄。      

Fabrication and mechanical properties of microalloyed and ceramic particulate reinforced NiAl-based alloys

NiAl-based alloys and their composites reinforced with in situ formed TiC and externally added ceramic particles are fabricated by hot-pressing. Their microstructures and mechanical properties are evaluated. Comparatively, the Ti- and/or C-alloyed NiAl and the ceramic particulate reinforced composites possess a significant improvement in both flexural strength fracture toughness at room temperature. Nevertheless, the NiAl–TiC-nano-Al₂O₃ composite has low strength, mainly due to the existence of residual porosity, inhomogeneous distribution and severe agglomeration of nano-scaled Al₂O₃ particle within the NiAl matrix.     

固溶处理对TiB2/6061复合材料硬度及耐磨性的影响

采用氟盐法制备了TiB₂质量分数为3%的原位合成TiB₂/6061复合材料,研究了固溶温度和固溶时间对复合材料硬度和耐磨性能的影响。结果表明:TiB₂颗粒弥散分布在6061铝合金基体中,明显细化6061铝合金基体晶粒。当固溶温度一定时,随固溶时间延长,复合材料的硬度和耐磨性可获得明显提高,但固溶时间在6~10 h时,复合材料的性能变化不显著。当固溶时间一定时,随固溶温度升高,复合材料硬度和耐磨性呈现先上升后下降的趋势。3wt%TiB₂/6061复合材料经530 ℃×10 h固溶处理后,硬度和耐磨性能最佳,相较于铸态硬度值提高了79.5％,磨损量减少了59.1%。固溶处理后复合材料的磨损表面犁沟变细变浅,材料脱落现象减少。     

Microstructural characterization of NiCr1BSiC laser clad layer on titanium alloy substrate

Laser cladding of NiCrBSiC powders on Ti–6Al–4V alloy substrate was carried out, and the microstructure of the laser clad layer was characterized by TEM and SEM. Results show that the phases of TiC, TiB₂, CrB and M₂₃C₆ were formed in situ in the clad layer. The TiC phase exists in the form of dendrites with two types of interface morphology including the non-faceted and the faceted one. The TiB₂ phase nucleates on the facets of TiC dendrites, and can grow to form a special morphology of microstructure in which the TiC dendrite is encased by the TiB₂ phase. The CrB and M₂₃C₆ phases exist in the form of rod-shaped morphology, inside which stacking faults could be observed. The clad layer matrix consists of primary γ_p-Ni dendrites and lamellar eutectics of γ_e-Ni+Ni₃B. The formation mechanism of the microstructure of the clad layer was discussed.     

氩弧熔覆原位合成TiC-TiB2复合抗氧化涂层

为了提高石墨电极的高温抗氧化性能,以钛粉和B₄C粉为原料,采用氩弧熔覆技术在石墨电极表面原位反应合成TiC-TiB₂复合涂层. 利用X射线衍射分析、蔡司电子显微镜和扫描电子显微镜对涂层的组织形貌和物相组成进行了分析,利用间歇法测试了TiC-TiB₂复合涂层的高温抗氧化性能. 结果表明,熔覆层由花瓣状的TiC颗粒和棒状的TiB₂颗粒组成,熔覆层与石墨基体热匹配性好,表面无裂纹和气孔等缺陷,且熔覆层具有良好的抗高温氧化性能,1 300℃高温氧化6 h,氧化增重率为0.546 mg/mm2·h-1.     

基于Ti中间层的B4C复合陶瓷扩散连接接头界面微观组织与力学性能

碳化硼(B₄C)复合陶瓷以其高硬度、高熔点、良好的耐磨性以及吸收中子能力的特性,广泛应用于制造防弹装甲材料,原子反应堆控制以及耐磨耐高温结构材料等领域.文中采用中间层Ti箔对碳化硼复合陶瓷(B₄C-SiC-TiB₂)进行扩散连接,研究了连接温度对连接界面组织及接头力学性能的影响.结果表明,在连接温度1300 ~ 1450 ℃下成功扩散连接了B₄C-SiC-TiB₂复合陶瓷,Ti与B₄C反应生成TiB₂和TiC.随着连接温度的升高,反应层变厚,而过厚的反应层会对接头的性能造成不利影响.在连接温度1300 ℃时,反应层的平均厚度约为5 μm,此时获得较高的接头抗剪强度100 MPa;在连接温度1450 ℃时连接层基本为TiB₂和TiC陶瓷相,此时扩散连接接头可以获得较高硬度(25.4 GPa).     

The impact characteristics of Ti–6Al–4V plates hardfacing by laser alloying NiAl+ZrO2 powder

This investigation considers the alloying of NiAl powders, with 0, 10, 20, 30, and 40 wt.% of ZrO₂ added, by the CO₂ laser upon Ti–6Al–4V base metals. Trial experiments are performed to obtain the optimum thickness of the powder, 0.1 mm, and the transverse speed, 1 mm/s, upon which the hardfacing process was based. The microstructures of the alloying layers were analyzed by OM, X-ray spectroscopy and SEM/EDS. The mechanical properties of the alloying layers were analyzed by micro-hardness and impact tests. The results indicated that the microstructure of the hardfacing layer was finer and its micro-hardness was higher than those of the base material. During the hardfacing process, NiAl and ZrO₂ powder were dissolved in a molten pool, reacted with other elements, and new phases were then formed. Impact tests revealed that the absorption of the vibration increased as the ZrO₂ added.     

Ti6Al4V合金表面氩弧熔覆原位合成TiC-TiB2增强钛基复合涂层组织与耐磨性

以B4C和Ni60A粉末为预涂材料,采用氩弧熔覆技术,在Ti6Al4V合金表面原位合成TiC与TiB₂增强相增强钛基复合材料涂层.运用XRD,SEM等分析手段研究了复合涂层的显微组织,利用显微硬度仪测试了复合涂层的显微硬度并用磨损试验机分析了其在室温干滑动磨损条件下的耐磨性能.结果表明,熔覆层组织主要由TiC和TiB₂组成,TiC颗粒和TiB₂颗粒弥散分布在基体上,TiC颗粒的尺寸为2~3μm,而呈长条状的TiB₂颗粒尺寸为3~5μm.显微硬度和耐磨性测试结果表明,该复合涂层显微维氏硬度高达1200MPa左右,复合涂层的耐磨性能比Ti6Al4V基体提高约20倍.     

电弧熔炼Ti6Al4V/B4C复合材料微观组织与力学性能

采用真空电弧熔炼技术制备了不同含量B₄C的Ti6Al4V/B₄C钛基复合材料,并采用光学显微镜、扫描电子显微镜、显微硬度计、静态压缩及拉伸测试等对其微观组织及力学性能进行了表征分析. 结果表明,电弧熔炼过程B₄C与钛基体原位反应生成TiB,TiC及TiB₂相,TiB呈现一维生长晶须状,TiC呈现颗粒状,在B₄C质量分数为10%时生成块状TiB₂,并可能会形成特殊的中空棱柱状结构Ti(B_xC_y)聚合物. 原位反应生成的TiB₂可显著提高钛基复合材料的显微硬度. 当B₄C质量分数为0.5%时,钛基复合材料原位反应生成的连续网状、均匀分布的TiB和TiC试样具有最优力学性能,试样最大抗压强度值达到1 990 MPa,最大压缩应变为35.5%,压缩性能超过熔炼钛合金,抗拉强度达到1 034 MPa,与熔炼钛合金材料相比提高近24%,但塑性有所降低,并随着B₄C含量增加,抗拉强度逐渐下降,其断裂方式由韧性断裂转变为脆性断裂.     

Microstructure of hot-pressed B4C–TiB2 thermoelectric composites

B₄C–TiB₂ thermoelectric composites were prepared via hot-pressing. The phase composition, microstructure of the samples were characterized by means of XRD, SEM and TEM. The composition of different phases, including grain boundary phase, was analyzed by means of EDS. The effects of the microstructure on the thermoelectric properties of the composites are discussed.