稀土元素的添加对原位生成的Ti-TiC-TiB复合材料抗磨损性能的影响

采用Ti 6Al 4V 5B4C和Ti 6Al 4V 5B4C 1Nd 两种成分的原始粉末, 反应热压后原位生成了Ti TiC TiB复合材料。经过X射线检测, 证明了试验中原位生成反应5Ti+B4C 4TiB+TiC的进行。采用摩擦磨损试验机检测了两种材料的抗磨损性能。通过扫描电子显微镜和电子探针分析了材料的磨损表面。结果表明, 添加稀土元素能提高材料的硬度, 韧性和抗磨损性能。     

不连续增强钛基复合材料的研究进展

不连续增强相能有效改善钛基体的力学性能，提高钛基体的耐磨性、高温强度和抗氧化性，拓宽了钛合金的应用领域。陶瓷增强相具有硬度高、耐磨性好、热稳定、成本低廉等优点，成为不连续增强钛基复合材料的首选增强相，其中使用最为广泛的是TiC颗粒和TiB纤维。纳米碳材料因具有高弹性模量以及高抗拉强度等优异性能，可有效改善复合材料的强度、塑性，被用来制备高比强度的钛基复合材料，近年来成为最具潜力增强体材料。本文从增强体材料的选择出发，归纳总结了近十年不连续增强钛基复合材料的研究进展，综述了不同增强体材料对钛基体组织与力学性能的影响以及强化机理，提出进一步的研究方向，为提高钛基复合材料的整体性能和扩大其应用范围提供一定的依据。     

Fatigue and fracture of damage-tolerant In Situ titanium matrix composites

In an effort to engineer damage-tolerant ingot metallurgy (IM) in situ titanium matrix composites with attractive mechanical properties, the fatigue and fracture properties of a range of high-modulus titanium alloys reinforced with TiB whiskers were examined. The strengthening effects due to elastic whisker reinforcement are quantified using shear lag and rule-of-mixture models. The effects of alloy composition and microstructure on the fatigue behavior of the in situ titanium composites will also be discussed.     

添加剂镍对原位合成TiB2-TiC复相陶瓷材料性能的影响

用TiH2，Ni和B4C作为原料，采用热等静压法制备了TiB2-TiC复相陶瓷材料，此方法工艺简单。成本较低。XRD研究表明在样品中只存在TiB2和TiC两相；TEM研究结果表明TiB2晶粒为规则的多边形和板条状，添加剂Ni位于TiB2/TiC交界处；显微硬度、断裂韧性和SEM断口形貌的研究结果表明添加剂Ni显著提高了TiB2-TiC复相陶瓷材料的综合性能。     

TiC晶须的制备及应用

TiC晶须以其优异的物理和化学性能具有重要的研究意义和实用价值.该文综述了国内外TiC晶须的最新研究进展,详细介绍了几种制备TiC晶须的典型方法,如碳热还原法、化学气相沉积法、原位合成法、溶胶-凝胶法等,并指出了这几种制备方法的优缺点,分析、讨论了TiC晶须的2种生长模型及机理;介绍了TiC晶须作为增强增韧相在陶瓷基复合材料、金属基复合材料中的具体应用情况,展望了TiC晶须的发展前景.     

Microstructural characterisation and mechanical properties of spark plasma-sintered TiB2-reinforced titanium matrix composite

Titanium and titanium matrix composites, reinforced with TiB₂ particles, have been synthesised by the spark plasma sintering method at 1050°C under 50?MPa pressure, using mixtures of 2.4?wt.-% TiB₂ and 97.6?wt.-% Ti powders. The changes in microstructural features and mechanical properties were investigated. XRD results and SEM observations confirm the formation of TiB whiskers as a result of the reaction between Ti and TiB₂. However, some unreacted TiB₂ particles have remained in the composite owing to the incomplete chemical reaction between matrix and additives. The measured mechanical properties demonstrate that the increase in hardness and tensile strength with TiB₂ addition is mainly attributed to the generation of TiB whiskers, increase in relative density and decrease in grain size, while the reduction in bending strength is possibly due to the plastic restraint imposed on the matrix by the TiB whiskers and unreacted TiB₂ particles.     

Mechanical properties of molybdenum disilicide based materials consolidated by hot isostatic pressing (HIP)

The influence of hot isostatic pressing (HIP) consolidation parameters on the mechanical properties of molybdenum disilicide (MoSi₂) reinforced with ductile and brittle reinforcements was studied. MoSi₂, MoSi₂-20 vol.% coarse and fine niobium powder and MoSi₂-20 vol.% silicon carbide whiskers consolidation by HIP at 1200–1400°C, 207 MPa, for 1 and 4 h were tested in compression for elevated temperature strength and creep resistance. Single-edge-notched specimens of the three materials were tested in a three-point bend configuration for fracture toughness. Mechanical properties were related with consolidation parameters and post-HIP microstructures.     

TiB whisker coating on titanium surfaces by solid-state diffusion: Synthesis,microstructure, and mechanical properties

The study demonstrates the feasibility of synthesizing TiB whiskers on titanium (Ti) surfaces by solid-state diffusion to form a hard and wear-resistant coating. The microstructural and mechanical properties of the TiB coating layer have also been investigated. The TiB coating was formed by the solid-state diffusion of boron (B) from a powder mixture containing amorphous boron, Na₂CO₃ powder, and charcoal (activated) powder. The diffusion process was carried out at various temperatures ranging from 800 °C to 1000 °C for various periods of time ranging from 1 to 24 hours. The amount of Na₂CO₃ in the mixture was also varied. It has been found that pristine and extremely fine TiB whiskers form on the surfaces of titanium, with the whiskers growing more or less normal to the surface. A maximum coating thickness of about 218 μm was observed for the pack diffusion conditions at 850 °C for 24 hours with 15 pct Na₂CO₃. The kinetics of TiB formation was found to follow the growth rates in bulk composites. The X-ray diffraction (XRD) patterns of the coatings revealed the dominant TiB peaks with a very few TiB₂ peaks, with small intensity at higher temperature and time. The surface hardness of the coated layer increased to a Vickers hardness of about 550 kgf/mm² due to the presence of TiB whiskers in the coating. It is shown that pack diffusion of boron in the solid state is a simple and very effective means of generating hard and wear-resistant coatings on titanium.     

原位合成TiB增强钛基复合材料的微观组织研究

在热力学计算纯钛粉与TiB2颗粒生成TiB条件的基础上，采用原位反应粉末冶金技术制备了TiB／Ti复合材料。试验结果表明，采用计算的反应条件可以实现纯钛粉与TiB2颗粒完全反应，反应生成物TiB呈晶须状，TiB晶须在基体中均匀分布，并与基体之间界面平整、干净。     

原位TiC颗粒强化的Fe-Cr-Ni基复合材料的拉伸性能

研究了原位TiC颗粒强化的Fe-26Cr-14Ni基复合材料的常温和高温拉伸性能,分析了该复合材料的断裂特征,结果表明,含5％和10％（体积分数,下同）的TiC复合材料的常温和高温综合拉伸性能明显高于基体合金;TiC含量为10％时具有最佳的高温拉伸性能,随着TiC体积分数的提高,复合材料的常温断裂由韧性断裂向脆性断裂转变,该复合材料的高温断口形貌主要呈现出韧性断裂的特征。     

Influence of reinforcement volume fraction and size on the microstructure and abrasion wear resistance of hot Isostatic pressed white iron matrix composites

The changes in the microstructure and wear resistance of a powder metallurgical high-Cr white iron after the incorporation of TiC particles were studied in the present work. Various reinforcement volume fractions and sizes were used in order to examine their influence on the three-body abrasion wear resistance. The experiments were carried out at three different austenitizing temperatures. The most important observation after a microstructural examination was the increased amount of martensite in the composites subjected to identical heat treatment procedures with the unreinforced alloy. The austenite-to-martensite transformation in the composites increased with the TiC volume fraction and with the austenitizing temperature. This indicates that the two parameters have a key role in the transformation mechanism, which seems to be mechanically induced. The increasing of martensitic transformation with the TiC content in the composites enhanced continuously the supporting ability of the iron alloy matrix to the TiC particles, which in turn increased the wear resistance of the composites. The abrasion wear resistance increased with the TiC volume fraction until the onset of spalling. However, in composites containing coarse reinforcements, spalling occurred earlier in the wear process. This decreased wear resistance significantly because spalled TiC particles contributed additionally to wear.     

Mechanical behavior of damage tolerant TiB whisker-reinforced in situ titanium matrix composites

The results of a systematic study of the effects of alloying and microstructure on the mechanical behavior of in situ titanium matrix composites are reported in this paper. In situ composites are produced by alloying with B which promotes the formation of TiB whiskers during rapid solidification processing. The composite powders are subsequently compacted and extruded to align the whiskers prior to systematic heat treatment in the β and/or α + β phase fields. The processing conditions for the development of in situ composites with attractive combinations of strength, ductility, damage tolerance and creep resistance are thus established. The improvements in the composite properties are rationalized using simple micromechanics principles. The paper highlights the potential for the microstructural design of composites using micromechanics and conventional physical metallurgy principles.     

Wear Behavior of Aluminum Matrix Hybrid Composites Fabricated through Friction Stir Welding Process

Effects of friction stir processing (FSP)parameters and reinforcements on the wear behavior of 6061-T6 based hybrid composites were investigated.A mathematical formulation was derived to calculate the wear volume loss of the composites.The experimental results were contrasted with the results of the proposed model.The influ-ences of sliding distance,tool traverse and rotational speeds,as well as graphite (Gr)and titanium carbide (TiC) volume fractions on the wear volume loss of the composites were also investigated using the prepared formulation. The results demonstrated that the wear volume loss of the composites significantly increased with increasing sliding distance,tool traverse speed,and rotational speed;while the wear volume loss decreased with increasing volume fraction of the reinforcements.A minimum wear volume loss for the hybrid composites with complex reinforcements was specified at the inclusion ratio of 50% TiC+50% Al2 O3 because of improved lubricant ability,as well as resist-ance to brittleness and wear.New possibilities to develop wear-resistant aluminum-based composites for different in-dustrial applications were proposed.     

Solidification paths and reinforcement morphologies in melt-processed (TiB + TiC)/Ti In Situ Composites

A novel in situ process was developed to produce titanium matrix composites reinforced with TiB and TiC of different mole ratios in which traditional ingot metallurgy plus self-propagation hightemperature synthesis (SHS) reactions between Ti and B₄C, graphite powder were used. Microstructures of (TiB+TiC)/Ti in situ composites were comprehensively characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Solidification paths were investigated using a differential scanning calorimeter (DSC). Results show that there is an apparent difference in morphologies of reinforcements. The reinforcements nucleate and grow from the melt in a way of dissolution precipitation. The different morphologies are related to their solidification paths and the particular crystal structure of the reinforcement. TiB grows along the [010] direction and forms short-fiber shape due to its B27 structure, whereas TiC with NaCl type structure grows in a dendritic, equiaxed, or near-equiaxed shape. The DSC results and analysis of the phase diagram yield three stages for the solidification paths of in situ synthesized titanium matrix composites: (1) primary phase, (2) monovariant binary eutectic, and (3) invariant ternary eutectic. The addition of graphite adjusts the solidification paths and forms more dendritic primary TiC. The addition of aluminum does not change the solidification paths. However, the reinforcements grow finer and lead to equiaxed or near-equiaxed TiC morphologies. The following consistent crystallographic relationships between TiB and titanium were observed by HRTEM, i.e., [010]_TiB//[ ]_Ti, (100)_TiB//( )_Ti, (001)_TiB//(0002)_Ti, ( )_TiB//( )_Ti and [001]_TiB//[ ]_Ti, ( )_TiB//( )_Ti, (200)_TiB//(0002)_Ti. The formation of the preceding crystallographic relationships is related to the growth mechanism of TiB. It also helps to minimize the lattice strain at the interfaces between TiB and the titanium matrix.     

Synthesis of ductile titanium-titanium boride (Ti-TiB) composites with a beta-titanium matrix: The nature of TiB formation and composite properties

The study focused on the in-situ synthesis of titanium (Ti)-titanium boride (TiB) composites with β phase in the matrix by reaction sintering of TiB₂ with Ti and alloying element powders. The goal was to examine the nature of TiB whisker formation in three different kinds of powder mixtures: (1) β-Ti alloy powders and TiB₂; (2) α-Ti powder, a master alloy (Fe-Mo) powder containing the β-stabilizing elements, and TiB₂; and (3) α-Ti powder, a β-stabilizing elemental powder (Mo or Nb), and TiB₂. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at processing temperatures ranging from 1100°C to 1300°C. The morphology, size, and distribution of whiskers were found to be influenced by the powder-packing conditions. A large particle-size ratio in bimodally packed mixtures led to the formation of a TiB monolithic layer around β grains. With a relatively finer starting powder, smaller size ratio, and trimodal packing arrangement, the TiB whiskers were found to be distributed more homogeneously in the matrix. The study also used the X-ray direct comparison method and the structure factor for the β phase to determine the volume fraction of TiB phase from X-ray data. Tensile tests and fractographic investigations were carried out on selected composites. The evolution of the composite microstructure, the influence of powder-packing variables, and the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed.     

Investigation of Production and Abrasive Wear Behavior of Functionally Graded TiB 2 /Al and TiB 2 /Al–4Cu Composites

In this study, it is aimed to investigate the production and abrasive wear properties of functionally graded TiB2/Al and TiB2/Al–4Cu composites. Using in situ technique, titanium di-boride (TiB2) particles are being spontaneously formed in liquid matrix, resulting in a “Al(l) + TiB2(S)” semisolid at 900 °C. The semisolid solidifies under a centrifugal force at 1500 rpm rotation speed in a steel mold to produce functionally graded composites. The properties of composites such as density, abrasive wear, hardness and microstructure were examined by dividing into four zones from the outside to the inside of the composite. Volume loss of composites were examined by using L16(4124) orthogonal design, considering some factors such as matrix type of composites, region of composites, abrasive particle size, sliding speed and sliding load according to Taguchi method. The results showed that both TiB2/Al and TiB2/Al–Cu composites had two regions: the TiB2-reinforced and non-reinforced regions. It was determined that the volume loss increased with increasing load, speed and abrasive particle size and decreased with increasing TiB2 particles reinforcement ratio.     

气固反应原位生成TiC颗粒增强钛基复合材料

以氢化脱氢钛粉为原料, 经冷等静压成型, 在一定温度下通过CH4和钛粉颗粒间的气固反应在钛粉表面原位生成均匀的TiC颗粒, 采用真空烧结技术制备得到氧含量(体积分数)低于0.2%的TiC颗粒增强钛基复合材料。研究表明, TiC颗粒体积分数比可通过气固反应温度和时间控制, 可获得较高体积分数(> 30%)的TiC颗粒增强钛基复合材料。TiC首先在钛粉颗粒表面形成, 烧结过程中, 钛粉颗粒明显阻碍TiC晶粒长大, 细化TiC晶粒; 同时, 过多的TiC颗粒也阻碍烧结过程中钛的自扩散, 降低烧结相对密度。钛粉压坯在700℃、CH4气氛下发生气固反应(30 min), 再经1300℃烧结后获得的相对密度为98.6%的烧结试样, 试样的综合力学性能较好, 抗拉强度为606 MPa, 延伸率达14.4%, 硬度为HV 442。值得注意的是, 较短时间的气固反应不能够保证压坯内外整体实现原位生成均匀TiC颗粒, 导致烧结试样内外组织的不均性。     

Transverse creep and stress-rupture of borsic-aluminum composites and borsic-aluminum composites containing stainless steel and titanium

The transverse creep and stress rupture behavior of a number of Borsic®-aluminum composites was investigated at temperatures from 200° to 400°C. The cpmposites studied consisted of nominally 50 vol pct Borsic fiber and included matrices of 6061, 2024, 2219, and 5052 aluminum alloys. The effect of heat treatment was studied in the heat-treatable alloys. Where transverse composite behavior differed from matrix alloy behavior, the difference was found to be due primarily to a change in fracture mode at higher matrix strength levels from matrix failure to one which involves longitudinal fiber splitting. Of the four basic matrix alloys tested, the best creep resistance was obtained with the 2024 matrix. Additional improvement of transverse creep and stress rupture resistance was realized by incorporating transverse reinforcements such as SAP alloy foil, titanium alloy foil, and 0.002 in. stainless steel wire in the composites. These reinforcements made possible good transverse properties at 400°C with density increases of ≤15 pct. The two best additions were 21 pctβ III titanium foil and 6 pct AFC-77 stainless steel wire. A transverse fracture mode incorporating longitudinal fiber splitting was documented and characterized, and its effect on composite behavior determined. The use of nonsplitting fibers such as 5.6 mil B and 5.7 mil Borsic in preventing this fracture mode was investigated.     

Mechanical Properties of Aluminium-Graphene Composite Synthesized by Powder Metallurgy and Hot Extrusion

The present work focuses on the development of multilayer graphene reinforced aluminium metal matrix composites by powder metallurgy followed by hot extrusion. Microstructure, grain size analysis and mechanical properties of hot extruded unreinforced aluminium and graphene reinforced aluminium composites are presented here. Microstructure shows uniform distribution of graphene throughout the matrix. Experimental results reveal significant increase in hardness as well as tensile strength of composite as compared to unreinforced aluminium. The improvements in properties are attributed to uniformly dispersed graphene sheets, an excellent interfacial bonding between graphene and aluminium matrix and grain refinement caused by the addition of graphene. Further, the strengthening mechanisms involved in the aluminum-graphene composite have been discussed. The fracture studies show the transition of ductile fracture in case of pure aluminium to brittle fracture in case of aluminium-graphene composites.