W丝/Zr基非晶合金复合材料动态拉伸断裂模式研究

采用霍普金森杆拉伸技术研究了W丝体积分数为80%的W丝/Zr基非晶合金复合材料的动态拉伸性能,通过扫描电镜研究了该复合材料动态拉伸断裂模式.结果表明:随着打击速度增加,复合材料动态拉伸强度和断裂应变总体呈上升趋势;复合材料的动态拉伸断裂模式以钨丝解理断裂为主导,伴随非晶合金基体产生脉纹状花样和钨丝劈裂;脉纹状花样的形态不同于在动态压缩条件下所形成的,不存在"尖脊"形貌.     

非晶复合材料制备与性能

总结了近年来本课题组在外加强化相非晶复合材料制备方面取得的主要研究结果。通过制备过程凝固控制获得了性能优异的非晶复合材料,其中金属W/Zr基非晶合金双连续相复合材料压缩强度达到3 450 MPa,压缩应变为48%;金属Ti/Mg基非晶合金双连续相复合材料压缩强度达到1 750 MPa,塑性应变为30%;8%Nb颗粒/Mg基非晶复合材料压缩强度达到900 MPa,塑性应变为12.1%;6%S iC颗粒/Zr基非晶复合材料压缩强度达到2 230 MPa,塑性应变为3%。     

陶瓷颗粒增强Zr基非晶合金复合材料高温变形行为研究

在非晶合金中添加第二相制备非晶合金复合材料能够有效地解决非晶合金室温脆性的问题,但第二相的引入对非晶基体高温变形行为造成的影响尚不明确。本研究在Zr₅₅Cu₃₀Al₁₀Ni₅非晶合金中添加两种不同的陶瓷颗粒Al₂O₃和Si₃N₄,通过放电等离子烧结法制备了一系列不同体积分数的陶瓷颗粒增强Zr基非晶合金复合材料。通过进行高温压缩试验,并建立多颗粒随机分布模型进行数值模拟,对其高温变形行为进行了系统性研究。结果表明,在421℃时,两种复合材料都表现为应力过冲后应变硬化;在441℃时,Al₂O₃增强的复合材料表现为屈服后应变硬化,对于Si₃N₄增强复合材料,当第二相体积分数小于25%时表现为屈服后应变硬化,当第二相体积分数大于25%时材料却表现为应力过冲后应变硬化。两种非晶合金复合材料的高温变形行为差异与增强相形貌以及增强相颗粒团聚...     

SiC泡沫陶瓷/Fe基双连续相复合材料的制备和性能

将SiC泡沫陶瓷氧化,用挤压铸造法制备SiC泡沫陶瓷/Fe基双连续相复合材料并对其退火,研究了制备工艺和SiC泡沫陶瓷的体积分数对其微观组织和力学性能的影响。结果表明,在1250℃氧化48 h后在SiC泡沫陶瓷表面生成了厚度为1 mm的SiO2反应阻挡层。在双连续相复合材料的制备过程中,SiO2反应阻挡层抑制Fe与SiC的化学反应,避免了脆性化合物Fe3Si的生成,改善了基体与增强体的界面,使复合材料的抗弯强度提高2倍,压缩强度提高18%。当SiC泡沫陶瓷的氧化时间增至72 h时,SiC泡沫陶瓷表面SiO2的厚度过大。SiO2与基体和增强体热膨胀系数不匹配,使复合材料内相界面间的残余应力增加,导致其性能下降。将SiC泡沫陶瓷/Fe基双连续相复合材料在600℃退火4 h,可降低复合材料中的残余应力,提高复合材料的性能。SiC的体积分数较低时,金属基体的桥接、偏转裂纹的作用比较大,复合材料的弯曲强度高,变形程度大。随着复合材料中SiC体积分数的增大,SiC骨架筋增粗,其承载能力加强,复合材料的压缩强度呈提高的趋势。     

Mg65CU20Zn5Y10多孔非晶的制备及性能

为提高镁基非晶合金的塑性应变能力,采用水冷铜模浇铸-拔丝造孔法制备了Mg65Cu20Zn5Y10多孔非晶合金,对Mg65Cu20Zn5Y10多孔非晶合金的组织、热稳定性和压缩性能进行了研究。结果表明,采用多孔芯水冷铜模制备出了直径6mm、长24mm的Mg65Cu20Zn5Y10多孔非晶合金;与镁基非晶合金相比,孔结构对其热稳定性没有影响;Mg65Cu20Zn5Y10多孔非晶合金在低应力作用下的塑性应变可达40%;Mg65Cu20Zn5Y10多孔非晶合金的断裂形貌呈脉状花样,属韧性断裂。     

Fe43Cr16Mo16C18B5Y2大块非晶合金的晶化行为及力学性能研究

采用铜模吸铸法制备出Fe43Cr16Mo16C18B5Y2块体非晶合金,并用XRD、SEM、DSC、硬度和压痕实验分别研究了该合金的结构、压缩断口形貌、晶化特征、硬度和断裂韧度.由热分析曲线得到玻璃转变温度(Tg)、晶化起始温度(Tx)和晶化峰值温度(Tp),这些特征温度具有明显的动力学效应.用Kissinger方法计算出不同升温速率下该Fe基块体非晶合金的玻璃转变激活能Eg、晶化激活能Ex、激活能Ep,结果表明该合金具有较高的热稳定性.力学实验结果表明,该块体非晶合金的硬度高达1178kg/mm2,断裂韧度为7.614MPa·m1/2,呈典型的脆性断裂,通过压缩断口形貌的观察发现该块体非晶合金的断裂呈现剪切断裂模式.     

TiZr基非晶/TC21双层复合材料的制备和力学性能

用渗流法制备TiZr基非晶/TC21钛合金双层复合材料，并对其微观组织和力学性能进行深入的研究。结果表明，TiZr基非晶(ZT3, Ti_32.8Zr_30.2Ni_5.3Cu₉Be_22.7)合金熔体与TC21钛合金之间的界面结合良好且有良好的润湿性。制备温度对双层复合材料的微观结构和力学性能有极大的影响。随着制备温度的提高，界面层的厚度和TC21钛合金的溶解量增加，非晶基体中枝晶相的体积分数增大、晶粒粗化。这种双层复合材料的强度随着温度的提高而降低，在室温下具有良好的弯曲塑性，其弯曲强度达到2177 MPa、动态压缩强度达到1326 MPa。     

新型复式连通SiC/390Al复合材料的制备和性能

以空心多孔SiC泡沫陶瓷为增强体,用挤压铸造法制备了新型复式连通双连续相SiC/390Al复合材料,研究了泡沫陶瓷骨架筋的结构对复合材料的影响,以及复合材料中的界面对力学性能的影响.结果表明,SiC空心多孔泡沫陶瓷与390Al复合后形成了复式连通双连续相复合材料,具有独特的互穿式界面结构,材料界面的结合优异.随着复合材料界面结合的加强和泡沫增强体的复合韧化,复合材料的屈服强度、压缩强度和弯曲强度明显提高,韧性显著增强.     

Ni基合金粉末及其非晶涂层的制备与表征

为解决非晶粉末价格昂贵、成型困难等问题,采用真空气雾化法制备了Ni FeCrMoNbBSi合金粉末,利用火焰喷涂焰流温度高、冷凝速度快有利于形成非晶相等特点,经火焰喷涂后制备了镍基非晶涂层。通过XRD、SEM、EDS、TEM等对粉末和涂层的相组织结构、表面形貌和微观特征进行了表征。结果表明:Ni FeCrMoNbBSi合金粉末形貌为球形或近球形,主要由晶体相FeNi3和Ni CrFe固溶体组成,非晶含量较少。制备的Ni基非晶涂层组织结构致密,主要由非晶相和Cr2Ni3金属间化合物组成,非晶含量可达70%(体积分数)。     

TiC颗粒增强非晶钛合金基复合材料的热稳定性

用单辊铜轮旋注法制备了TiC颗粒增强Ti45Zr5Cu25Ni20Sn5非晶合金基复合材料.发现在Ti45Zr5Cu25Ni20Sn5非晶合金中加入TiC颗粒可以提高合金的热稳定性.     

2D-C/SiC复合材料低温动态Z向压缩性能

采用Hopkinson压杆试验装置,对2D-C/SiC复合材料进行了低温条件下的Z向动态压缩性能试验研究,低温条件通过控制酒精和液氮的配比系数得到,通过改变波形整形器几何尺寸的方法来实现恒应变率加载,以得到准确、可信的试验结果。试验结果表明: 由于复合材料内部含有大量初始微缺陷,2D-C/SiC复合材料在低温动态加载条件下呈现伪塑性行为,其破坏时并未表现出典型的脆性破坏,而是在应力达到压缩强度时出现了显著的应变软化现象,在经历了较大的变形后才最终破坏。随着温度的降低,复合材料的动态Z向压缩强度增加,但失效应变减小。2D-C/SiC复合材料在低温环境下,其内部纤维和基体之间界面结合力增强,同时强的界面结合力可以导致高的压缩强度。     

Processing and properties of Al–Li–SiCp composites

Al–Li–SiC_p composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 mm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macroand microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ^' (Al₃Li) and S^' (Al₂CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition.     

增强体含量对SiC_W/SiC层状陶瓷复合材料强韧性的影响

采用流延-化学气相渗透(TC-CVI)工艺制备SiC晶须(SiC_W)/SiC层状陶瓷复合材料,研究了SiC_W含量对层状陶瓷复合材料力学性能和微观结构的影响,探讨了SiC_W/SiC层状陶瓷复合材料的强韧化机制。结果表明:TC-CVI工艺能够有效提高复合材料中晶须含量(40vol%),减少制备过程对晶须损伤,所制备的SiC_W/SiC层状陶瓷复合材料具有合适的层内及层间界面结合强度。随着SiC_W含量增加,层状陶瓷复合材料的密度和力学性能均有明显提高。含40vol%晶须的SiC_W/SiC层状陶瓷复合材料的密度、弯曲强度和断裂韧性均比含25vol%晶须的分别提高了8.4%、30.8%和26.7%。断口形貌中能够观察到层间及层内的裂纹偏转,层内的裂纹桥接和晶须拔出等,这些为主要的增韧机制。高含量SiC_W及合适的层间和层内界面结合强度,对提高SiC_W/SiC层状陶瓷复合材料强韧性有明显作用。     

界面过渡层对SiC/Al双连续相复合材料性能的影响

研究了界面过渡层对SiC/Al双连续相复合材料性能的影响.结果表明,界面过渡层降低了复合材料中的残余应力,改善了界面的结合,提高了复合材料的压缩性能.当界面过渡层中SiC的体积分数接近50%时,复合材料的压缩强度最高,塑性最好,但弹性模量较低.界面过渡层的存在改变了复合材料的弯曲断裂机制.SiC原始泡沫增强的复合材料在断裂时,增强体SiC泡沫先断裂,基体后破坏,断裂表面凹凸不平;含界面过渡层的复合材料断裂时,过渡层的外侧界面先被撕开,内侧界面结合良好,基体与增强体同时断裂,断口平整.     

Processing and properties of Al–Li–SiCp composites

Al–Li–SiC_p composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 μm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macro- and microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ^′ (Al₃Li) and S^′ (Al₂CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition.     

冷热循环处理对钛基非晶合金摩擦学性能的影响EI北大核心CSCD

钛合金的耐磨性较差,在钛合金活动部件表面制备钛基非晶合金涂层是一种保持钛合金优势又提升其耐磨性的选择。采用X射线衍射仪、差示扫描量热仪、SEM、摩擦磨损试验机,对冷热循环处理前后钛基块体非晶合金的组织结构与摩擦行为进行比较研究。结果表明:经过冷热循环处理后的钛基块体非晶合金仍然保持着完全非晶态,弛豫焓提升11%。冷热循环处理后钛基非晶合金的平均纳米硬度从6.84 GPa降低到6.59 GPa,平均弹性模量从118.70 GPa降低到103.43 GPa,但硬度与弹性模量的比值增大。冷热循环处理后,钛基块体非晶合金在5 N和10 N的载荷下磨损率减小了约10%。与TC4合金相比,其在5 N和10 N载荷下的磨损率分别减小了20%和50%。TC4合金由于硬度较低,呈现较为严重的黏着磨损。冷热循环处理后,钛基非晶合金的磨损机制从铸态的磨粒磨损为主向磨粒磨损、黏着磨损和氧化磨损共同作用转变,且随着载荷的增大,黏着磨损减轻,磨粒磨损占据主导。因此,冷热循环处理是提升钛基块体非晶合金摩擦学性能的一种有效方法。     

Statistical analysis for strength and spatial distribution of reinforcement in SiC particulate reinforced aluminum alloy composites fabricated by die-casting

Statistical analysis for strength and spatial distribution of reinforcement in die-cast SiC_p/Al alloy composites was performed in order to predict the reliability of composites. Microstructural analysis was also done to determine the critical features of the composites. Die-casting was carried out using the preheated die at the casting temperature range of 620–750°C. It was found that the SiC pacticulates were homogeneously dispersed in die-cast Al matrix alloy, resulting from the refinement of dendritic cell size due to rapid cooling rate. The tensile strength of die-cast SiC_p/Al alloy composites was higher than that of die-cast Al matrix alloy. Also, the tensile strength was slightly increased with increasing SiC particulate volume fraction at the casting temperature range of 650–700°C. It was concluded that the die-cast temperatures of 750 and 700°C are optimum condition for the distribution of SiC particulates in consequence of good fluidity of melt for 10 and 20 vol.% SiC_p/Al alloy composites, respectively. However, the strength scattering of composites was increased with increasing SiC particulate volume fraction. For the statistical evaluation of strength, the maximum Weibull modulus of die-cast SiC_p/Al alloy composites, which was obtained at the cast temperature of 700°C, was 29.6 in Al matrix alloy, 22.2 in 10 vol.% SiC_p and 14.2 in 20 vol.% SiC_p, respectively.     

Compressive behaviour of SiC/ncsc reinforced Mg composite processed through powder metallurgy route

In this present work nano coconut shell charcoal (ncsc) and silicon carbide (SiC) particulates were reinforced with AZ31B Mg alloy and suitable magnesium composite was developed by using the powder metallurgy technique followed by hot extrusion. Density measurement of the Mg composites revealed that the addition of ncsc significantly improved the density of the composites and porosity measurement showed minimal porosity. The microstructure of the composites showed even distribution of the ncsc in the AZ31B/3SiC Mg composite. The compressive and impact behaviour of the samples were characterized, the results showed that on increasing the weight percentage of ncsc in AZ31B/3SiC/0.5ncsc Mg composites the mechanical properties such as ultimate compressive strength, 0.2% yield strength, ductility and impact strength decreased. The scanning electron microscope (SEM) analysis of fractured surface of AZ31B Mg alloy and AZ31B/3SiC/0.5ncsc Mg composites showed quasi-cleavage fracture. The presence of ncsc above 0.5 wt% composites revealed mixture of quasi cleavage planes and some dimples.     

Effects of crystalline particles on mechanical properties of strip-cast Zr-base bulk amorphous alloy

Effects of crystalline phase particles formed in a strip-cast Zr-base bulk amorphous alloy on strength, ductility, and fracture toughness were investigated by directly observing microfracture processes using an in situ loading stage installed inside a scanning electron microscope chamber. The compressive and fracture toughness test results indicated that strength, ductility, and fracture toughness of the strip-cast amorphous alloy were higher than those of the as-cast monolithic amorphous alloy, although the strip-cast alloy contained a considerable amount (4.5 vol.%) of hard, brittle crystalline particles. According to the in situ microfracture observation, crystalline particles were easily cracked under low stress levels, acted as blocking sites of shear band or crack propagation, and provided initiation sites of multiple shear bands. Thus, the improvement of mechanical properties in the strip-cast alloy could be explained by mechanisms of (1) blocking of crack propagation, (2) formation of multiple shear bands, and (3) crack deflection by crystalline particles.