SiC纤维增强钛基复合材料空心结构成形研究

采用箔材刻槽法制备连续纤维增强钛基复合材料(SiC/Ti)面板,通过分析不同复合工艺参数条件下的纤维/基体界面和基体微观组织,获得了优化的制备工艺:925℃/100 MPa/1 h.利用SiCf/Ti复合材料沿垂直纤维方向具有大变形的能力,将超塑成形/扩散连接技术(SPF/DB)与SiCf/Ti复合材料的复合技术相结合...     

KD-S和KD-Ⅱ SiC_f/SiC复合材料的制备、微观结构及性能（英文）

以KD-S和KD-Ⅱ型碳化硅(SiC)纤维编织件为增强体,通过先驱体浸渍裂解工艺制备了以热解炭(PyC)为界面涂层的三维(3D)结构SiC_f/SiC复合材料,系统研究了SiC_f/SiC复合材料的微观结构及性能间的关系。结果表明:KD-S和KD-Ⅱ型SiC纤维均具有晶粒尺寸为8～15 nm的多晶结构;两种SiC_f/SiC复合材料的断口表面均出现了纤维拔出现象,说明两种SiC纤维增强的SiC_f/SiC复合材料均具有典型的伪塑性断裂行为。KD-S SiC_f/SiC复合材料的弯曲强度、弹性模量和断裂韧性分别达到(955.0±42.8) MPa,(110.3±1.7) GPa和(28.5±2.8) MPa·m~(1/2),明显高于KD-ⅡSiC_f/SiC复合材料,这归因于近化学计量比的KD-S型SiC纤维具有较高的模量和耐温性能。由于KD-S和KD-Ⅱ型SiC纤维的结构及成分差异,导致KD-S型SiC纤维表面的PyC界面涂层呈现光滑的多层有序结构,而KD-Ⅱ型SiC纤维表面的PyC为疏松颗粒状结构。     

镁基复合材料高温变形研究进展

自20世纪80年代以来,不同类型(颗粒、晶须、纤维等)的增强镁基复合材料日益增多并得到了广泛的研究。镁基复合材料可设计性较强,且具备突出的力学性能与物理性能,包括低密度、高比刚度、较低的热膨胀系数、良好的阻尼性能、优异的抗震降噪能力及优良的电磁屏蔽性能等,在航空航天、军工制造、汽车电子、建筑用材及生物医用等各领域有着巨大的发展前景,被视作在先进技术领域颇具竞争力的一种轻质金属基复合材料。然而,镁及镁合金的晶体结构为密排六方型,室温下独立的滑移系相对较少,相应地,镁及镁合金具备较差的塑性加工能力。同时,作为硬质相的增强相,与基体镁合金之间的物理化学性能相差较大,存在一定的不兼容性。增强相的添入进一步恶化了镁基复合材料的塑性加工能力,这在很大程度上限制了镁基复合材料的使用。因而,开展关于镁基复合材料在高温变形等方面的研究工作十分重要。国内外关于镁基复合材料高温变形行为方面的科研工作大部分聚焦于不同的工艺参数对高温变形行为的影响、高温变形时发生的加工硬化及动态再结晶现象、建立相应的本构模型等方面。镁基复合材料常见的高温变形方式主要有五种,分别为超塑性变形、高温压缩、热循环变形、高温蠕变及高温二次变形。研究者们针对不同的高温变形方式开展了大量的研究工作,并取得了较为显著的研究成果。其中,高温压缩由于变形工艺相对简单而得到了更为广泛深入的研究。近年来,研究者们不仅探究了不同高温变形方式对镁基复合材料微观组织与性能的影响,还探究了应变量、温度、应变速率等变形条件对镁基复合材料高温变形行为的影响,更深入地探究了镁基复合材料在高温变形过程中的微观组织演变规律与相应的变形机制,结合数值分析构建了相应的本构模型,为镁基复合材料高温变形工艺的制定与优化提供了强有力的理论支持,有助于实现对镁基复合材料微观组织与性能的有效调控。本文综述了镁基复合材料高温变形的不同类型,阐释了镁基复合材料高温变形的本构方程及软化机理,并展望了今后镁基复合材料在高温变形方面的发展方向。     

液-固两相区压缩变形对SiCw/6061Al复合材料组织和性能的影响

研究了液固两相区压缩变形对SiC_w/6061A l 复合材料组织和性能的影响。结果表明, 压缩变形温度对变形后复合材料中晶须长径比、取向, 复合材料组织的致密性、均匀性和界面结合状态均有不同程度的影响。复合材料组织的变化又影响到复合材料的性能。复合材料高温大变形后性能的变化是评价复合材料高温塑性成形加工工艺的最重要指标。通过分析复合材料的组织和性能, 从而确定了复合材料最佳压缩变形工艺。     

镍基高温合金初始织构对电辅助拉伸宏微观行为的影响

目的研究织构对镍基高温合金电辅助成形的影响规律。方法通过准静态拉伸与电辅助拉伸对比实验,研究了不同初始织构对镍基高温合金电辅助成形宏观力学行为以及微观组织演化的影响规律。结果当初始织构为易变形织构时,拉伸后的纤维织构峰值较低,而电辅助拉伸过程中焦耳热使得试样温度升高,变形抗力得到下降,在一定程度上增大了纤维织构的强度。当初始织构为难变形织构时,材料变形抗力大,拉伸后纤维织构峰值较高,但材料变形过程晶粒细化程度高,缺陷的增多导致电辅助成形过程中焦耳热更为明显,焦耳热导致的高温使得难变形晶粒变形更为协调,最终的纤维织构强度有所下降。结论不同的初始织构对电辅助成形宏微观行为有较大的影响,因此合理利用织构在电辅助成形过程中的影响以完善电辅助成形工艺十分重要。     

NiTi形状记忆合金热变形行为及加工图

目的应用Gleeble 3500热模拟试验机,研究Ni Ti形状记忆合金在变形温度650~1000℃、应变速率0.001~10 s~(–1)条件下的热变形行为,并基于动态材料模型构建合金的加工图。方法采用包含Arrhenius项的Z参数法建立该合金的本构关系数学模型,计算变形激活能,构建应变量为0.7和1.2时的加工图,并结合微观组织观察验证加工图预测结果的准确性。结果 Ni Ti合金热变形激活能Q为227.9 k J/mol。根据加工图可知,所研究Ni Ti合金的失稳变形工艺参数范围分别为:650~930℃,0.1~10 s~(–1)和930~1000℃,0.3~10 s~(–1),对应的失稳变形机制分别为局部流动和机械失稳;适宜的变形参数工艺范围为:750~800℃,0.01~0.03 s~(–1)和850~900℃,0.01~0.03 s~(–1),对应的变形机制为动态再结晶。结论研究结果可为Ni Ti合金成形工艺制度的制定和优化提供理论依据。     

变形条件对 Mg-10 Gd-3 Y-Zr 镁合金组织及力学性能的影响

采用 Gleeble2000 热力学模拟试验机对 Mg-10 Gd-3 Y-Zr 镁合金进行了不同变形条件下的单向热压缩试验,研究变形温度、变形程度、变形速率等变形条件对合金显微组织及力学性能的影响,优化成形工艺参数。 结果表明,对于 Mg-10 Gd-3 Y-Zr 镁合金,合理的等温成形应在较高的变形温度(410 ~ 440 ℃ ) ,较低的变形速率(0 . 001 ~ 0 . 01 s^-1) ,较大的变形程度( ≥25% ) 下进行。     

颗粒增强钛基复合材料等温热变形与组织演化规律

目的突破难变形颗粒增强钛基复合材料热加工关键技术,以满足航空航天、武器装备等领域对轻量化耐高温钛基复合材料的战略需求。方法采用等温热变形技术研究颗粒增强钛基复合材料(TiB+La_2O_3/Ti)的热变形行为及微观组织演化规律,在变形温度为850~1100℃、应变速率为0.001~1 s~(-1)的条件下,建立该复合材料的本构方程及热加工图,结合微观组织演化规律分析,确定该复合材料等温热变形最佳加工工艺范围。结果增强体的加入,使钛基复合材料的流变应力和变形激活能提高,缩小了有效加工区间;材料热加工图中存在2个功率耗散率峰值区域,分别位于α+β两相区(900~950℃,0.003~0.1 s~(-1))和β单相区(1075~1100℃,0.3~1 s~(-1));在两相区易于发生连续动态再结晶,而单相区则对应于β晶粒的"项链"再结晶和片状α相的动态回复。结论该难变形复合材料等温热变形的最佳工艺范围为温度900~950℃、应变速率为0.003~0.1 s~(-1)。     

30%Mo/Cu-Al2O3复合材料的热压缩变形行为

利用Gleeble-1500热力模拟试验机,在温度为450～750℃、应变速率为0.01～5s-1、总应变量0.7的条件下,对30%Mo/Cu-Al2O3复合材料高温塑性变形过程中的动态再结晶行为及其热加工图进行研究和分析。实验结果表明30%Mo/Cu-Al2O3复合材料高温流动应力-应变曲线主要以动态再结晶软化机制为特征,峰值应力随变形温度的降低或应变速率的升高而增加;在真应力-应变曲线基础上,建立的30%Mo/Cu-Al2O3复合材料高温变形本构模型较好地表征了其高温流变特性;同时,利用30%Mo/Cu-Al2O3复合材料DMM加工图分析了其变形机制和失稳机制,确定了热加工工艺参数为变形温度650～750℃,应变速率0.01～0.1s-1。     

管类件定径挤压极限变形程度的数值模拟

分析了管类件定径挤压成形工艺，借助于有限元软件Deform-3D平台，对不同参数组合的45^#管类件定径挤压工艺进行了有限元数值模拟。给出了成形极限范围和不同参数对极限变形程度的影响规律。     

Interfacial control of uni-directional SiCf/SiC composites based on electrophoretic deposition and their mechanical properties

Interfacial control of uni-directional SiC_f/SiC composites were performed by EPD, and their mechanical properties at room temperature were evaluated. The effect of the thickness of carbon interphase on SiC fibers by EPD on mechanical properties of uni-directional SiC_f/SiC composites was also investigated. The average thickness of carbon coating on SiC fibers increased from 42 nm to 164 nm with an increase in the concentration of colloidal graphite suspension for EPD. Dense SiC_f/SiC composites were achieved and their fiber volume fraction was 47–51%. The SiC_f/SiC composites had a bending strength of 210–240 MPa. As the thickness of carbon coating was below 100 nm, the SiC_f/SiC composites (SC01 and SC02) fractured in almost brittle manner. In contrast, the SiC_f/SiC composites (SC03) showed a pseudo-ductile fracture behavior with a large number of fiber pullout as the thickness of carbon coating was above 100 nm. The fracture energy of SC03 was 3–4 times as high as those of SC01 and SC02 and the value was about 1.7 kJ/m². In consideration of the results of mechanical properties, the thickness of carbon coating on SiC fibers should be at least 100 nm to obtain high-performance SiC_f/SiC composites. The fabrication process based on EPD method is expected to be an effective way to control the interfaces of SiC_f/SiC composites and to obtain high-performance SiC_f/SiC composites.     

Microstructure, mechanical properties and reaction mechanism of KD-1 SiCf/SiC composites fabricated by chemical vapor infiltration and vapor silicon infiltration

Three-dimensional (3D) KD-1 silicon carbide fiber reinforced silicon carbide matrix (KD-1 SiC_f/SiC) composites were fabricated by a combining chemical vapor infiltration (CVI) and vapor silicon infiltration (VSI) process. The microstructure and mechanical properties of the resulting KD-1 SiC_f/SiC composites were studied. The results show that the resulting SiC_f/SiC composites have high bulk density and low open porosity (<6%). The mechanical properties of the resulting SiC_f/SiC composites firstly increase and then decrease with decreasing the open porosity of the SiC_f/C composites. The KD-1 SiC fibers were not severely deformed and adhered to the matrix with a weak interface during the VSI process. As a result, the composites exhibit non-catastrophic failure behavior. Additionally, the diffusion mechanism for the VSI process was also investigated in our work.     

Fabrication of SiCf/SiC composites by chemical vapor infiltration and vapor silicon infiltration

Three-dimensional (3D) silicon carbide fiber reinforced silicon carbide matrix (SiC_f/SiC) composites, employing KD-1 SiC fibers (from National University of Defense Technology, China) as reinforcements, were fabricated by a combining chemical vapor infiltration (CVI) and vapor silicon infiltration (VSI) process. The microstructure and properties of the as prepared SiC_f/SiC composites were studied. The results show that the density and open porosity of the as prepared SiC_f/SiC composites are 2.1 g/cm³ and 7.7%, respectively. The SiC fibers are not severely damaged during the VSI process. And the SiC fibers adhere to the matrix with a weak interface, therefore the SiC_f/SiC composites exhibit non-catastrophic failure behavior with the flexural strength of 270 MPa, fracture toughness of 11.4 MPa·m^1/2 and shear strength of 25.7 MPa at ambient conditions. Moreover, the flexural strength decreases sharply at the temperature higher than 1200 °C. In addition, the thermal conductivity is 10.6 W/mk at room temperature.     

Microstructure and properties of SiCw/6061 aluminium alloy composites after compression at temperatures around solidus of matrix

Abstract

The effect of compressive deformation at temperatures around the solidus of the matrix on the microstructure and properties of SiC_w/6061 aluminium alloy composites was investigated. It was found that the temperature, strain rate, and amount of deformation affect whisker distribution and breakage, densification and uniformity of composites, and SiC_w/matrix alloy interfacial bonding. The microstructural evolution due to compression affects the properties of the composites, which is considered to be the most important aspect for evaluating high temperature plastic forming of the composites. The optimum parameters for compressive deformation were determined by analysing the microstructure and the properties of the composites.     

Mechanical behavior of SiCf/SiC composites with alternating PyC/SiC multilayer interphases

In order to tailor the fiber–matrix interface of continuous silicon carbide fiber reinforced silicon carbide (SiC_f/SiC) composites for improved fracture toughness, alternating pyrolytic carbon/silicon carbide (PyC/SiC) multilayer coatings were applied to the KD-I SiC fibers using chemical vapor deposition (CVD) method. Three dimensional (3D) KD-I SiC_f/SiC composites reinforced by these coated fibers were fabricated using a precursor infiltration and pyrolysis (PIP) process. The interfacial characteristics were determined by the fiber push-out test and microstructural examination using scanning electron microscopy (SEM). The effect of interface coatings on composite mechanical properties was evaluated by single-edge notched beam (SENB) test and three-point bending test. The results indicate that the PyC/SiC multilayer coatings led to an optimum interfacial bonding between fibers and matrix and greatly improved the fracture toughness of the composites.     

The effect of fabrication processes on the mechanical and interfacial properties of SiCf/Cu–matrix composites

Three groups of SiC_f/Ti/Cu composites were prepared under conditions of 650 °C + 105 min (sample 1#), 750 °C + 85 min (sample 2#) and 840 °C + 50 min (sample 3#), respectively, by foil-fiber-foil method (FFF), and their room temperature tensile strengths were established. The aim is to model the reactive bonding states between Ti and SiC fiber and between Ti and Cu when Ti is used as interfacial adhesion promoters in SiC_f/Cu–matrix composites. The fracture surfaces, SiC_f/Ti interfaces and Ti/Cu interfaces were investigated by scanning electron microscopy (SEM), optical microscopy and energy dispersive spectroscopy (EDS). The tensile tests show that the tensile strengths of samples 1# and 2# are not obviously enhanced due to the weak bonding strength between SiC fiber and Ti, while those of sample 3# are achieved above 90% of ROM (the rule of mixtures) strength because of excellent bonding between SiC fiber and Ti. However, there are distinct Ti/Cu interfacial reaction zones after the three processes, which are approximately 5.4, 9.0 and 13.3 μm thick, respectively. The Ti/Cu interfacial reaction products are mainly distributed in four layers. In samples 1# and 2#, the products are predicted to be Cu₄Ti, Cu₃Ti₂, CuTi and CuTi₂ according to their chemical compositions determined by EDS, while in sample 3#, the products are Cu₄Ti, Cu₄Ti₃, CuTi and CuTi₂. Additionally, the relationships between the thickness of Ti interlayer and its reaction with C and Cu are also discussed, and an optimal thickness of Ti is introduced.     

Microstructure and grain growth of the matrix of SiCf/Ti–6Al–4V composites prepared by the consolidation of matrix-coated fibers in the β phase field

The microstructural characteristics in the matrix of SiC_f/Ti–6Al–4V composites prepared by consolidation of the matrix-coated fibers in the high-temperature β single-phase field were investigated using both experimental and modelling methods. Some of the critical microstructure features, like volume fraction of component phases, composition of matrix alloys and matrix morphology were systematically studied, providing valuable insight into the microstructural characteristics in the matrix of SiC_f/Ti–6Al–4V composites. In order to assist in understanding the grain growth occurred in the matrix during consolidation processing, a theoretical model was developed. Excellent agreement between theoretical and experimental results was achieved.     

Effects of particle size and properties on the microstructures,mechanical properties,and fracture mechanisms of 7075Al hybrid composites prepared by squeeze casting

To investigate the effects of particle size and properties on the mechanical properties of 7075Al matrix composites, hybrid composites reinforced using three different reinforcement combinations, 40 vol. % 7 μm SiC_p with 5 vol. % 7 μm SiC_p, 35 μm SiC_p, and 35 μm Ti, were prepared using squeeze casting. The failure mechanisms and the microstructure–property relationships of hybrid composites were studied using SEM, TEM, and tensile tests. The composite containing Ti particles achieved the highest tensile strength of 626 MPa and an elongation of 1.2 %. Fracture mechanism analyses imply that the reduced strength for the 35 μm SiC_p-containing composite are caused by the inefficient load transfer capability resulting from the preferential breakage of larger-sized SiC_p particles during the deformation process. In contrast, micro-zones formed by Ti particles at the center and matrix alloy with few dislocations around release stress and deform synergistically during deformation, which decreases the breakage of SiC_p and improves the plastic deformation ability of the matrix alloy, resulting in a good combination of strength and ductility.     

A study of the strength of P/M 6061Al and composites during high strain rate superplastic deformation

Metal Matrix Composites (MMCs) are potential candidate materials in the aerospace and automobile industries because of its attractive properties, in particular, their high specific properties, and Superplastic forming (SPF) is a good solution to the problems in the forming process of MMCs due to their low ductility resulting from the incorporation of reinforcement. High strain rate superplasticity (HSRS) is attractive for industrial applications because superplastic forming at high strain rates can reduce forming time greatly. The strength of P/M 6061 Al and 6061 Al/SiC_p (3 m) composites during superplastic deformation at temperatures of 853 K–871 K and a high strain rate of 0.1 s^–1 has been studied in this paper. Experimental results presented a softening effect by the SiC_p reinforcement. Mechanical and microstructural analyses show that the decrease in the strength during high strain rate superlastic (HSRS) deformation is associated with the decreased grain size of the Al matrix with increase of the SiC_p volume fraction or the extrusion ratio, and the occurrence of liquid phase. The formation of the liquid phase was related to segregation of the solute atom during HSRS deformation.     

Interface microstructures in Ti-based composites using TiB2/C-coated and uncoated SiCf after short-term thermal exposure

The extent of interfacial reaction after short-term thermal exposure during vacuum plasma spraying (vps) and vacuum hot-pressing (vhp) of Ti-based metal-matrix composites (mmcs) using TiB₂/C-coated and uncoated SiC fibres has been investigated by a combination of scanning and transmission electron microscopies. There is no interfacial reaction after short-term thermal exposure during vps manufacture of SiC_f/Ti mmcs using either TiB₂/C-coated or uncoated SiC_f. There is only limited interfacial reaction after short-term thermal exposure during vhp manufacture of SiC_f/Ti-6Al-4V mmcs using TiB₂/C-coated SiC_f. In the initial stage of the interfacial reaction, TiB needles are formed by preferential nucleation and growth at β particles and grain boundaries in the Ti-6Al-4V matrix.