Si3N4／SiC复合陶瓷粉末的研制

研究了添加晶种的碳热还原ＳｉＯ２法制取Ｓｉ３Ｎ４／ＳｉＣ复合粉末的工艺。发现反应温度的升高、反应时间的延长、原料ＳｉＯ２粉比表面的增大、添加Ｓｉ３Ｎ４晶种以及提高Ｎ２流速，均有利于Ｓｉ３Ｎ４、ＳｉＣ相含量的增加。当ＳｉＯ２：Ｃ为１：２，加入１０Ｗｔ％Ｓｉ３Ｎ４品种时，在１３５０℃下于Ｎ２流速为０．４ｍ３·ｈ－１气氛下反应４ｈ，可得到平均粒度为０．４６ｍ，含Ｎ２３．９ｗｔ％、Ｃ６．２５Ｗｔ％、Ｏ２．９０ｗｔ％的Ｓｉ３Ｎ４／ＳｉＣ超细复合粉末。     

燃烧合成大尺寸Si_3N_4陶瓷的研究

研究了大尺寸Ｓｉ粉坯在高压氮气中的燃烧行为，通过调整工艺参数，获得了完全氮化的Ｓｉ３Ｎ４陶瓷多孔坯体。研究表明，“后燃烧氮化”是大尺寸试样中部得以氮化完全的主要原因，并提出了燃烧合成Ｓｉ３Ｎ４的燃烧波区结构模型。     

用天然石英粉制备氮氧化硅粉末

以天然石英粉为原料，先进行活化预处理，然后在１３５０℃左右进行碳热还原氮化，制备了氮氧化硅粉末。实验结果表明：氮化过程中ＳｉＯ２的转化率及产物中氮氧化硅（Ｓｉ２Ｎ２Ｏ）的含量与ＳｉＯ２的活化程度、氮化温度及添加剂等因素有关，其中氮化温度以１３５０℃为佳；随着ＳｉＯ２活化程度的提高，其转化率也提高；添加少量的ＳｒＯ，可以进一步提高ＳｉＯ２的转化率。此外，还分析了ＳｉＯＣＮ系统中气体分压对Ｓｉ２Ｎ２Ｏ形成的影响。     

颗粒增强Al—4%Mg复合材料在等轴晶凝固过程中的颗粒推挤

研究了Ｓｉｃ，Ａｌ２Ｏ３，ＳｉＯ２颗粒增强Ａ－４％Ｍｇ复合材料的在凝固过程中，颗粒的种类、粒度对颗粒推挤导致颗粒分布均匀的影响，提出在等轴晶凝固条件下，颗粒推挤的强烈程度由等轴晶粒和颗粒的质量比确定，理论预测与试验结果吻合良好。     

颗粒增强Al－4％Mg复合材料在等轴晶凝固过程中的颗粒推挤

研究了ＳｉＣ，Ａｌ＿２Ｏ＿３，ＳｉＯ＿２颗粒增强Ａｌ—４％Ｍｇ复合材料在凝固过程中，颗粒的种类、粒度对颗粒推挤导致颗粒分布不均匀的影响。提出在等轴晶凝固条件下，颗粒推挤的强烈程度由等轴晶粒和颗粒的质量比确定。理论预测与试验结果吻合良好。     

Si_3N_4－钢铁钎接用银－铜－钛钎料及其钎接工艺

研究了合金型Ａｇ－Ｃｕ－Ｔｉ钎料成分对Ｓｉ_３Ｎ_４浸润性及钎接温度对该系钎料钎接Ｓｉ_３Ｎ_４－钢铁的钎接强度的影响。用该工艺进行Ｓｉ_３Ｎ_４电热塞中Ｓｉ_３Ｎ_４发热体与金属外套的钎接，经综合测试可知满足Ｓｉ_３Ｎ_４电热塞技术要求。     

Si3N4复合陶瓷材料的微观组织和断裂机制

使用ＡＥＭ和ＨＲＥ他添加纳米ＳｉＣ颗粒和同时添加纳米ＳｉＣ颗粒及ＳｉＣ晶须的两种Ｓｉ３Ｎ４复陶瓷材料的微观组织和断裂机制。结果表明,部分ＳｉＣ颗粒分布在ＳｉＣ晶内,ＳｉＣ晶须分布在Ｓｉ３Ｎ４晶粒之间,ＳｉＣ颗粒和晶须与Ｓｉ３Ｎ４界面之间不存在第二相组织,非晶组织大多分布在Ｓｉ３Ｎ４三叉晶界。断裂裂纹主要沿晶界和相界面扩展,也可能穿过少数Ｓｉ３Ｎ４晶粒。当裂纹扩展遇到ＳｉＣ颗粒和／或ＳｉＣ晶须时,会     

弥散质点和SiC颗粒复合强化Al基复合材料：Ⅰ.制备和微观结构

采用纯Ａｌ粉、Ｃ粉和ＳｉＣ颗粒进行械合金化和热处理，经冷压实后直接进行挤压，成功地制备了Ａｌ４Ｃ３、Ａｌ２Ｏ３弥散质点和ＳｉＣ颗粒复合强化Ａｌ复合材料、金相显微镜、透射电镜和高分辨电镜观察表明，ＳｉＣ颗粒与Ａｌ基体具有较好的界面结合，其在基体中分布的均匀性受基体粉末特性的影响Ａｌ２Ｏ３含量较低且尺寸细小。Ｘ射线衍射和透镜分析难以确定。Ａｌ４Ｃ３为尺寸细小（直径约０．２μｍ，长度约０．２μｍ）的棒状     

Si3N4—钢铁针接用银—铜—钛钎料及其钎接工艺

研究了合金Ａｇ－Ｃｕ－Ｔｉ钎料成分对Ｓｉ３Ｎ４浸润性及针接温度对该钎料钎接Ｓｉ３Ｎ４－钢铁的钎接强度的强度。用该工艺进行了Ｓｉ３Ｎ４发热体与金属外套的钎接。经综合测试可知满足Ｓｉ３Ｎ４电热塞技术要求。     

SiC颗粒弥散强韧化Si3N4陶瓷刀具材料

对ＳｉＣ颗粒弥散强度韧化氮化硅陶瓷刀具材料的组成,结构及性能进行了研究,结果表明,ＳｉＣ颗粒的加入使材料的温度,韧性及硬度匀比纯Ｓｉ３Ｎ４陶瓷有显著提高,通过对其显微结构的分析,发现ＳｉＣ颗粒的加入使材料的显微结构明显改善能有效地阻止β－Ｓｉ３Ｎ４晶粒的异常生长,有利于形成的均匀细小的组织结构,同时,对ＳｉＣ颗粒在Ｓｉ３Ｎ４基体中的增韧机理进行了探讨。     

阴极电压和供氮方式对纯氮离子渗氮的影响

分别研究了在500、600、650和700 V阴极电压条件下采用连续供气抽真空和间歇供氮闭炉的方式进行纯氮离子渗氮的工艺及机理.通过对间歇供氮闭炉离子渗氮层显微组织、相组成和硬度梯度的测定与分析,计算和验证了该工艺中N2分子临界离解能.结果表明,纯氮离子渗氮的活性氮原子来自于经阴极位降区加速的高能N 2与中性N2分子间的非弹性碰撞,离解N2分子的N 2离子临界能为48.64 eV,相应的阴极电压门槛值为650 V.纯氮离子渗氮工艺除要求阴极电压高于650 V外,间歇供气闭炉渗氮也是必备条件,在一定温度和足够高的阴极电压下,只有采用间歇供氮闭炉方式进行离子渗氮,从N2分子才能离解出足够多的活性氮原子,使试样表面产生明显的渗氮效果.     

Improvement of Mechanical Properties of Martensitic Stainless Steel by Plasma Nitriding at Low Temperature

A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 h at 350℃ by means of DC- pulsed plasma in 25%N2＋ 75%H2 atmosphere. The microstructure, phase composition, and residual stresses profiles of the nitrided layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitridied surfaces were also studied. The fatigue life, sliding wear, and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-on-disc wear tester, and a solid particle erosion tester. The results show that the 350℃ nitrided surface is dominated by c-Fe3N and ON, which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, the fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350℃ because plasma nitriding produces residual compressive stress inside the modified layer.     

高温气相反应合成金红石型纳米TiO2颗粒的研究

在高温气相反应器中,利用掺 ＡｌＣｌ３的 ＴｉＣｌ４氧化反应制备金红石型纳米 ＴｉＯ２颗粒研究了氧气预热温度、反应器尾部氮气流量、反应温度、停留时间等对 ＴｉＯ２颗粒大小的影响结果表明：提高氧气预热温度和加大反应器尾部氮气流量对控制产物粒径有利, ＴｉＯ２粒径随反应温度升高和停留时间延长而增大当反应温度为１３７３Ｋ, ＡＩＣｌ３与ＴｉＣｌ４摩尔比为 ０．２５、停留时间为１．７３ｓ时,纯金红石相纳米ＴｉＯ２颗粒的粒径分布为 ３０－５０ｎｍ．     

Effect of nitriding on the electrochemical behaviour of Ti‐Al‐Mn alloy

The effect of technological conditions of nitriding such as process time duration and chemical composition of saturating medium, on the corrosion behaviour of nitrided coatings in 14 M solution of sulphuric acid was analyzed. The investigations were done on the alloy Ti‐5,0 Al‐2,0 Mn. The nitriding was carried out in nitrogen both at atmospheric pressure and rarefied nitrogen pressure (1 Pa) at the temperature 850°C and time processing in the range from 5 to 20 h in nitrogen‐containing gas only, and in powder electrode graphite and nitrogen‐containing gas. It was shown that technological conditions of nitriding determine the protective properties of nitrided coatings. It was indicated that the optimal structure of the nitride layer for best corrosion protection is the thin nitride TiN_x with high surface quality and a gas‐saturated layer. Nitriding in graphite powder effects positively the protective properties of nitride coatings due to reducing the nitride‐forming process.     

Solid Solution Nitriding Technology of 15Cr-7.5Mn-2.6Mo Duplex Stainless Steel

NEW DEVELOPMENT of stainless steel mainlyoccurs in area of nitrogen-containing austenitic steeland austenitic-ferritic duplex steel.It has been proposedthat a nitrogen-alloyed steel can be considered as anhigh nitrogen steel(HNSs),when the nitrogenconcentration is higher than0.4wt%in austenitic steelsand higher than0.08wt%in martensitic steels'M1.Butthis concept has been developed for the newmanufacturing technologies of HNS,such as pressureor powder metallurgy.In addition,the chemical…     

钛气体渗氮的数值模拟

根据修正的Fick第二定律,对钛渗氮工艺进行数值模拟,研究氮气压、渗氮温度和氮化时间因素对渗氮工艺的影响,得到了不同工艺参数下渗层深度和氮的浓度分布曲线,为渗氮工艺参数的优化设计和渗氮过程的自动控制提供参考.     

The influence of surface microcracks and temperature gradients on the rf plasma nitriding rate

Rf plasma nitriding processes have been used recently for surface treatment. 304 Austenitic stainless steel has been nitrided using an inductively coupled rf plasma. High rates of nitriding and relatively high microhardness have been achieved. The effect of plasma power and plasma processing time on the rate of nitriding and the microstructure was investigated. A high nitriding rate of 3 μm²/s and a microhardness value of 1800 HV0.1 were achieved under optimum plasma conditions. The interpretation is based on a new approach that the microcracks in the surface, at a certain ambient temperature and plasma, can create traps for the active nitrogen species. The nitrogen concentration and temperature gradient can also draw some of the nitrogen species towards the bulk side. The microhardness can be explained in terms of the high concentration of nitrided phases created under the surface of the treated samples.     

A Numerical Model of Nitriding of a Gadolinium Specimen and Its Further Destruction during Storage

A numerical model of nitriding of an isotropic gadolinium specimen and its states during further storage under normal conditions (room temperature and atmospheric pressure) is developed. The model is implemented on the basis of the principles of thermoelasticity and mass transfer. The dynamics of distribution of nitrogen (N) and gadolinium nitride (GdN) in the specimen, which represents an additional phase formed during nitriding of the specimen, is considered. An algorithm of numerical solution of model equations is given.     

内凝胶工艺结合碳热氮化法制备ZrN纳米粉体

采用内凝胶工艺制得无定形的氧化锆凝胶与炭黑均匀混合的前驱体粉末,获得的前驱体在氮气条件下进行碳热氮化处理后得到氮化锆(ZrN)纳米粉体。结合热重/差式扫描量热分析(TGA/DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等手段,对内凝胶前驱体的热处理行为、所得产物的物相组成、微观形貌及显微结构等进行了表征。研究结果表明,氮化温度的升高有利于氮化程度的提高,1400℃氮化温度下可得到纯相纳米ZrN粉体;此外,碳的引入在热处理过程中起到了必要的还原作用,且碳的加入量需要适当,C/Zr摩尔比接近2是获得纯相ZrN粉体产物较为合适的条件。     

机械合金化制备含氮ODS奥氏体不锈钢粉末

以纯金属粉末Fe、Cr、Ni、W、Ti和纳米Y2O3为原料(成分配比为Fe-18Cr-8Ni-2W-1Ti-0.35Y2O3),通过在氮气氛围下高能球磨的方式实现混合粉末的合金化。在球磨时间不变的情况下,改变氮气压力,获得含氮量不同的合金钢粉末。研究了氮含量对粉末形貌、粒度、粉末相组成、晶格畸变程度以及合金化效果的影响。球磨后的粉末在900和1100℃下退火,研究了退火温度及含氮量对退火后粉末相组成的影响。