Dissolution-precipitation mechanism of self-propagating high-temperature synthesis of TiC-Cu cermets

The mechanism of self-propagating high-temperature synthesis (SHS) of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope (SEM) with energy dispersive X-ray (EDX) spectrometry, and the combustion temperature was measured. The results showed that the com- bustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solu- tion. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.     

Preparation of ZrB2 Ceramics by Self-propagating High-temperature Synthesis and Hot Pressing Sintering

ZrB2 ceramics were prepared by self-propagating high-temperature synthesis（SHS） and were sintered by hot pressing（HP）.The effects of the granularities and doses of raw materials in Zr-B2O3-Mgon SHS process and product were investigated.XRD and combustion temperature curves prove that the ideal SHS reactants of Zr-B2O3-Mg are 50μm Zr powder,75μm B2O3 powder and 400μm Mg powder with 45% excessive.The particle sizes of SHS product,acid-leached product,sintered product are 2-5μm,0.5-2μm,2-10μm respectively.Chemical analysis indicates that the acid-leached product consists of ZrB2（94.59%）,ZrO2（3.87%）,and H3BO3（1.54%）,The sintered product has a relative density of 95.4%.     

TiC/Ti-Al基复合材料的燃烧合成

为了改善Ti-Al金属间化合物的脆性,利用SHS/PHIP工艺制备了TiC/Ti-Al基复合材料.理论分析表明,绝热温度随C质量分数的增加而呈升高趋势,当体系中碳的质量分数≥2%时,该体系能完成自蔓延过程.采用电子扫描显微镜,X射线衍射仪对合成产物进行了分析.结果表明,合成产物中除存在基体相Ti3Al和TiAl和增强相TiC外,还存在许多三元相Ti3AlC和Ti2AlC相;随着Al质量分数的增加,增强相的形貌由颗粒状逐渐变成棒状或片状;复合材料的硬度和压缩强度随C质量分数的增加逐渐增加,但密度及相对密度随C质量分数的增加呈先增加后降低的趋势.当C的质量分数达到4%时,其实际密度和相对密度均达到最大.     

TiB2-Cu复合材料SHS工艺的人工神经网络优化

利用3×5×1的3层BP神经网络模型对SHS法制备TiB2-Cu基复合材料过程中的工艺参数进行优化.将SHS工艺的3个主要参数--延迟时间、高压压力和高温保压时间作为人工神经网络的输入,合成产物的相对密度作为网络的输出,利用单参数动态搜索算法对SHS工艺参数进行了优化.结果表明训练样本和检验样本的网络实际输出值与相应的试验值均非常接近,TiB2-Cu基复合材料的SHS最佳工艺参数是延迟时间为6.8 s,高压压力为360 MPa,高温保压时间为9.2s.     

TiB_2-Cu复合材料SHS工艺的人工神经网络优化

利用3×5×1的3层BP神经网络模型对SHS法制备TiB_2-Cu基复合材料过程中的工艺参数进行优化。将SHS工艺的3个主要参数——延迟时间、高压压力和高温保压时间作为人工神经网络的输入,合成产物的相对密度作为网络的输出,利用单参数动态搜索算法对SHS工艺参数进行了优化。结果表明训练样本和检验样本的网络实际输出值与相应的试验值均非常接近,TiB_2-Cu基复合材料的SHS最佳工艺参数是延迟时间为6.8s,高压压力为360 MPa,高温保压时间为9.2s。     

Microstructural evolution of Al-8.59Zn-2.00Mg-2.44Cu during homogenization

The microstructural evolution and phase transformations of a high-alloyed Al-Zn-Mg-Cu alloy （Al-8.59Zn-2.00Mg-2.44Cu,wt%） during homogenization were investigated. The results show that the as-cast microstructure mainly contains dendritic α（Al）, non-equilibrium eutectics （α（Al） ＋ Mg（Zn,Al,Cu）2）, and the θ （Al2Cu） phase. Neither the T （Al2Mg3Zn3） phase nor the S （Al2CuMg） phase was found in the as-cast alloy. The calculated phase components according to the Scheil model are in agreement with experimental results. During homogenization at 460℃, all of the θ phase and most of the Mg（Zn,Al,Cu）2 phase were dissolved, whereas a portion of the Mg（Zn,Al,Cu）2 phase was transformed into the S phase. The type and amount of residual phases remaining after homogenization at 460℃ for 168 h and by a two-step homogenization process conducted at 460℃ for 24 h and 475℃ for 24 h （460℃/24 h ＋ 475℃/24 h） are in good accord with the calculated phase diagrams. It is concluded that the Al-8.59Zn-2.00Mg-2.44Cu alloy can be homogenized adequately under the 460℃/24 h ＋ 475℃/24 h treatment.     

置氢TC4钛合金等温锻造叶片组织演变规律

为了降低钛合金叶片的锻造温度和改善其组织性能,基于氢致钛合金高温增塑机理,将热氢处理技术应用于钛合金叶片的等温锻造成形工艺中.观察和对比分析了未置氢TC4钛合金和置氢TC4钛合金叶片等温锻造后的组织以及真空除氢热处理和普通热处理工艺下的组织演变.实验结果表明:置氢降低了TC4钛合金叶片的等温锻造载荷,除氢热处理后组织得到改善,获得了含有细小、等轴α晶粒的双态组织.确定了置氢量为0.25%(质量分数)的TC4钛合金适宜的热处理工艺为:锻后在750℃真空脱氢保温5h,900℃退火1h后再450℃时效4h.     

Microstructural evolution of a heat-treated H23 tool steel

The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures (...     

Microstructural evolution of ECAPed 1050 alloy under magnetic annealing

Hardness and microstructure evolutions in 1050 aluminum alloy prepared by equal-channel angular pressing （ECAP） were inves- tigated by hardness testing, optical microscopy, and transmission electron microscopy after samples were annealed at different temperatures for 1 h both in the absence and presence of a 12-T magnetic field. The results showed that the hardness of samples after magnetic annealing were lower than that of samples after normal annealing at 150-250℃, but it was higher than that of samples after normal annealing at 〉250℃. During annealing, the rate of softening was faster, and the grains were more homogeneous in 8-ECAPed samples than in 2-ECAPed samples. A rapid grain growth occurred when 2-ECAPed samples were annealed at high temperature （〉300℃）. The magnetic field enhanced the mobility of dislocations and grain boundaries. A more homogeneous grain size was observed in samples prepared under an applied magnetic field.     

SIMA法制备AZ91半固态坯料枝晶衍变规律的研究

研究了应变诱发熔化激活法(SIMA)制备AZ91半固态坯料枝晶演变规律.挤压后,AZ91组织结构为白亮拉长的初生α相和分布在其间的黑色共晶相.由于变形不充分,在试棒中心垂直于挤压方向仍有较大的初生α相存在.575℃等温重熔过程中,首先发生再结晶,伴随液相向再结晶产生的晶界渗透,导致枝晶破碎.随着等温保温时间的增加,组织转变为细小的球状α相,均匀分布在液相中.等温保温10m in时,α相由于组织的球化和粗化过程而变得更为圆整粗大.     

Microstructural evolution and mechanical properties of aging high nitrogen austenitic stainless steels

The microstructural evolution of 18Cr18Mn2Mo0.77N high nitrogen austenitic stainless steel in aging treatment was investigated by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that hexagonal intergranular and cellular Cr2N with a=0.478 nm and c=0.444 nm and body-centered cubic intermetallic χ phase with a=0.892 nm precipitate gradually in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular Cr2N pre...     

自蔓延高温合成技术的发展——材料制备的一项新技术

介绍了自蔓延高温合成技术的国内外发展现状，基础研究，最新研究动向以及技术应用前景。     

自蔓延高温反应合成NiCuZn铁氧体粉料的研究

以碳粉作为SHS反应的燃料合成(Ni0.2Cu0.2Zn0.6O)1.02(Fe2O3)0.98铁氧体粉料,通过XRD、SEM和VSM等检测手段,研究了C粉含量和氧气压力对NiCuZn铁氧体烧结样品的物相、形貌及磁性能的关系.研究表明,当氧气压力为0.2 MPa时,C质量分数为5%时,可获得铁氧体化较完全的铁氧体料粉,其饱和磁化强度为45.5 Am2/kg;随着C含量增加,产物中有ZnO相的出现,饱和磁化强度降低.当C质量分数为15%时,随着氧气压力的增大,铁氧体尖晶石相的衍射峰逐渐变锐,晶形转变趋于完整.     

自蔓延高温合成镍铜锌铁氧体粉体研究

为了研究低成本大批量生产制备NiCuZn铁氧体的方法,采用自蔓延高温合成(SHS)工艺制备了Ni0.25Cu0.25zn0.5Fe1.96O3.94粉体,将铁氧体粉体分别在800℃、850℃、900℃进行热处理.以XRD、SEM、TG-DSc、振动样品磁强计(VSM)等手段分别对产物的物相、微观结构和磁性能进行研究.结果表明,SHS制备的NiCuZn铁氧体粉体经900℃热处理后可以转变成单一的尖晶石相,所得铁氧体粉体结构完整,矫顽力达到最小值,Hc=72.3Oe,同时饱和磁化强度达到最大值,Ms=68.34emu/g.     

自蔓延高温合成TiB2微粉的热力学计算

从热力学上对Mg-Ti-B-O体系的自蔓延反应进行了理论分析,计算了稀释剂MgO、TiB2含量和预热温度对反应绝热温度的影响.结果表明,随着稀释剂MgO、TiB2含量和预热温度的不同反应绝热温度也不同,在同一预热温度下,随着稀释剂含量的增加绝热温度降低;同一体系中在稀释剂含量相同时,随着预热温度的升高绝热温度也升高;随着预热温度的不断升高,燃烧反应能自我维持的稀释剂的临界值也逐渐升高.     

陶瓷复合钢管热应力的有限元计算

用有限元方法计算了陶瓷基复合钢管的温度场及残余热应力,并分析了热应力对陶瓷裂纹形成的影响.在计算中,考虑了钢管的塑性变形和材料物理参数随温度的变化.     

Synthesis of Ni/Al System Intermetallic Compound Under the Influence of Pulsating Electric Current

1　IntroductionBecauseofitshighmeltingpoint(16 38℃ ) ,lowden sity(5 .9g cm3 ) ,goodthermalconductivity(4 - 8timestoNi basedthermalloy) ,satisfactoryoxidationresistance ,uniquehigh temperatureproperty (yieldstrengthgrowswithrisingtemperatureinsometemperaturerange) ,NiAlintermetalliccompoundisattractiveasapotentialmaterialforhightemperatureapplications .Theseapplicationsin cludeitsuseinturbinebladesinaircraftenginesorinstationarygasturbines .Self propagatingHigh temperatureSynthesis(SHS)hass…     

Preparation of ZrB_2 Ceramics by Self-propagating High-temperature Synthesis and Hot Pressing Sintering

1Introduction Self propagatinghigh temperaturesynthesis(SHS)isanattractivetechniquethatutilizesthehighheatofexother micreactionsbetweentherawmaterialstoproduceavariety ofceramicmaterials.Oncetheexothermicreactionswereinitiated,asufficientheatisreleasedtha…