Residual Stresses and Deformation Behaviour in a SiC_p/Al Composite

Experiments were conducted to determine theresidual stresses with X-ray diffraction in the ma-trix of a SiC/Al composite after different thermaltreatments,and to investigate the stress-straincharacteristics and fracture behaviour of the com-posite.It was found that there existed a tensileresidual stress in the matrix and both thermal cy-cling between room temperature and 350℃ and lowtemperature treatment in liquid nitrogen reducedthe residual stress.The results of the strengthdifferential effect and Bauschinger effect were con-sistent with the results of residual stressmeasurements.The tensile residual stresses in the Almatrix enhanced the strength differential effect.Themagnitude of Bauschinger effect is greater for a testinitially started in compression than that in tension.     

Stability of Phases in SiC and Si_3N_4 Whisker Formation

The stability of the phases in equilibrium is calculated and discussed in order to analyse and predict thereactions in SiC and Si_3N_4 whisker formation.Equilibria among SiC,Si_3N_4,Si_2N_2O,SiO_2 and the gas phaseare evaluated at different C activity,N_2 pressure,and temperature.According to the phase stabilitydiagrams,Si_3N_4 whisker was formed with the increase of N_2 pressure and decrease of C activity;SiC whiskerwas stable with the increase of C activity and decrease of N_2 pressure.In order to control the impure phasesduring the whisker formation,O_2 partial pressure is the most important factor.     

MC-C-O体系在超高温条件下相平衡的热力学分析

从热力学角度出发,采用工程数学软件Matlab计算出了在涉及超高温(2073 K以上)范围的宽温域内一些典型过渡金属碳(硼)化物与氧反应的△GO,以及相应的平衡氧分压;在此基础上绘制了2500 K时ZrC-ZrO2体系和SiC-SiO2体系的氧化物蒸气压图以及界面蒸气压随温度的变化曲线.依据上述热力学数据,可以了解不同碳化物的氧活性和平衡氧分压随温度的变化规律,以及ZrC-ZrO2和SiC-SiO2体系氧化物蒸气压特别是界面蒸气压的大小,对于深入了解改性C/C复合材料和超高温陶瓷的超高温氧化行为,特别是对于改性C/C复合材料中有效的抗氧化添加剂的选择有理论指导意义.     

Oxidation of pre-oxidized GH128 alloy implanted with Ce^＋ at 1 000 ℃

The influence of Ce implantation into preformed scales with a dose of 1 ×10^17 ions/cm^2 on the subsequent oxidation behavior of GHl28 alloy at 1000 ℃ in air was investigated. The pre-oxidation was carried out at 1000 ℃ in air for l h and 5 h respectively. Cr2O3, NiO and NiCr2O4 formed on the surface of all specimens. Ce implantation decreased the subsequent oxidation rate of both the alloy and the l h pre-oxidized alloy, however, had no effect on that of the 5 h pre-oxidized alloy. The beneficial effect was most obvious in the directly implanted alloy. During the cyclic oxidation for 600 h, Ce implantation for all specimens with or without preferential oxidation played a similar beneficial effect on the oxide spallation resistance. The results indicate that Ce incorporated into the oxide scales affects the diffusion of the reaction species to some extent, the wavy interface and small grain structure make a significant contribution to improving the spallation resistance of the oxide scales.     

Ti3Al基合金表面两种Cr1-xAlxN(x=0.18,0.47)涂层的热腐蚀性能

利用磁控反应溅射的方法在Ti3Al基合金表面制备了两种不同铝含量的Cr0.82Al0.18N与Cr0.53Al0.47N涂层,测试了这两种涂层在800℃(NR2SO4+25 mass%K2SO4)熔融盐膜百的热腐蚀动力学,并采用X射线衍射仪和带能谱的扫描电镜分析腐蚀产物相组成以及微观结构.结果表明,两种涂层均可降低Ti3Al基合金的热腐蚀速率;涂层热腐蚀产物主要为具有保护性的Cr2O3和θ-Al2O3混合氧化膜,θ-Al2O3的含量随着涂层中Al含量上升递增;和θAl2O3相比,Cr2O3在熔融硫酸盐中的稳定性更好,Cr0.82Al0.18N涂层抗热腐蚀性能优于Cr0.53Al0.47N涂层.     

片状晶Ti2SnC的制备

采用Ｔｉ、Ｓｎ和石墨粉末为原料，利用固液相反应用成功地制备出片状晶Ｔｉ２ＳｎＣ粉末。实验结果表明，所制备出的Ｔｉ２ＳｎＣ带有明显的取向性。应用Ｘ射线衍射及扫描电镜技术对Ｔｉ２ＳｎＣ粉末相进行成分及形貌分析和表征。     

β-SiC晶须的孪晶构型观察SCIEI

利用透射电子显微镜研究了气—液—固(VLS)法生长的β—SiC晶须中的孪晶构型。在竹节状的SiC晶须中,β—SiC节与含高密度堆垛层错(或一维无序)的节之间孪生相连,其李晶界为{111}_β;同时还观察到有的β-SiC节被{111}_β孪晶界分为两节。此外,在晶须的头部及分叉处还观察到了孪晶界平行晶须轴向的孪晶结构。利用选区电子衍射和像衍衬分析发现,这种双晶SiC晶须的孪晶面平行于基体的{001}_M。     

银在原子氧环境中的氧化行为

利用石英晶体微天平（QCM）、扫描电镜（SEM）和X射线衍射仪（XRD）对暴露在原子氧地面模拟装置中的银箔的表面氧化行为进行了研究.结果表明银在原子氧中的氧化分为两个阶段：在开始氧化过程中表面形成了一层较厚的Ag2O膜,由于氧化膜内较大的生长应力,使得氧化膜起皱、开裂和剥落;氧化过程的第二阶段为氧化膜顶层AgO的形成,AgO是由Ag2O和O反应生成的.     

连接温度、压力和保温时间对Ti3SiC2/Ni扩散连接接头性能的影响

利用Gleeble 3500热模拟实验机,在800～1100 ℃、10～90 min和6～20 MPa条件下对Ti3SiC2和Ni进行真空扩散连接.通过正交实验,研究了连接温度、连接压力和高温保温时间对试样连接强度的影响,优选出最佳工艺参数.结果表明,扩散连接工艺参数显著影响Ti3SiC2/Ni接头的剪切强度.在1000℃、10 min和20 MPa实验条件下,获得的Ti3SiC2/Ni接头的剪切强度达到(121±7)MPa,接近Ti3SiC2陶瓷的剪切强度.     

OBSERVATION OF TWIN CONFIGURATIONIN β-SiC WHISKERS

利用透射电子显微镜研究了气—液—固(VLS)法生长的β—SiC晶须中的孪晶构型。在竹节状的SiC晶须中,β—SiC节与含高密度堆垛层错(或一维无序)的节之间孪生相连,其李晶界为{111}_β;同时还观察到有的β-SiC节被{111}_β孪晶界分为两节。此外,在晶须的头部及分叉处还观察到了孪晶界平行晶须轴向的孪晶结构。利用选区电子衍射和像衍衬分析发现,这种双晶SiC晶须的孪晶面平行于基体的{001}_M。