REACTIVE DIFFUSION BETWEEN Si AND NbC AT 1300℃

ＲＥＡＣＴＩＶＥＤＩＦＦＵＳＩＯＮＢＥＴＷＥＥＮＳｉＡＮＤＮｂＣＡＴ１３００℃Ｃ．Ｒ．Ｋａｏ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｃａｌＥｎｇｉｎｅｅｒｉｎｇＮａｔｉｏｎａｌＣｅｎｔｒａｌＵｎｉｖｅｒｓｉｔｙＣｈｕｎｇＬｉ，Ｔａｉｗａｎ）Ｊ．Ｗｏｏｄｆ...     

难熔金属碳化物Cr_3C_2、VC、WC、TaC、NbC及Ti(C、N)粉中硫的测定

研究了燃烧──—电导法测定金属陶瓷添加剂Cr3C2；VC；WC；TaC；NbC及Ti（C、N）粉中硫的测定条件，建立了分析方法．方法相对标准偏差5％左右，仪器的灵敏度为3X10－6，最低检测限为1ppm．     

TEM Investigations of Fine Niobium Precipitates in HSLA Steel

Commercially produced 0.03 % C, 0.08 % Nb, 0.01 % Ti high strength low alloyed (HSLA) steel in the form of 20 mm thick plates was investigated. The steel was thermomechanically processed and the mechanical properties of the steel were evaluated by tensile testing. Using analytical and high resolution transmission electron microscopy the distribution, morphology, composition, crystal structure and particle size of niobium and titanium carbonitrides were observed and identified in these steels. The distribution of the precipitates was found to be nearly random, with occasional occurrence of precipitation free zones. Complex agglomerates with a cubic TiN seed crystal overgrown by a cubic NbC particle were the most commonly observed precipitates. Further TEM analysis in the accelerated cooled and tempered specimens in 1/4 plate thickness did not reveal any evidence that additional precipitation in the ferrite occurred. Precipitation in ferrite was only detected after subsequent cold deformation and tempering of the same samples. By a combination of EFTEM, STEM, HRTEM in addition to EDX spectroscopy, a large population of strain induced NbC precipitates with fcc crystal structure ranging in size down to 2 nm were identified in the ferrite matrix.     

电脉冲处理对FeMnSiCrNiNbC合金NbC析出及记忆效应的影响

研究了电脉冲处理对FeMnSiCrNiNbC合金形状记忆效应的影响,并对其微观机理进行初步探讨.结果表明,Fe17Mn5Si8Cr5Ni0.5NbC合金经5%预变形,300 V,1 Hz电脉冲处理13次后形状回复率达到80%,比800℃时效1000s获得的最大值提高12%.SEM分析表明,电脉冲处理可在极短的时间内加速诱导大量、细小的NbC颗粒在基体内析出,进而有效地改善了合金的记忆性能并提高了效率.     

30CrNiMo铸钢件冲击性能不合格原因分析

针对30CrNiMo铸钢件调质后冲击吸收能量不合格的问题,通过断口分析、金相检验、硬度测试、化学成分分析等方法对30CrNiMo铸钢件冲击吸收能量不合格原因进行了分析。结果表明,30CrNiMo铸钢件冲击断口为沿晶断口。金相检验发现淬火态晶粒不均匀,存在混晶现象。Nb在原奥氏体晶界处偏聚形成NbC,一方面能降低晶界的活动性,对晶界迁移起阻碍作用,另一方面,形成较多的第二相粒子起钉扎晶界、巩固晶界遗传的作用,最终导致奥氏体晶粒粗化后,钢的韧性—脆性转变温度升高,钢在室温进行冲击时得到脆性穿晶断口和低的冲击性能。     

原位生成NbC颗粒增强镍基激光熔覆层

激光熔覆技术是金属材料表面强化和改性的有效方法之一。利用该技术,在A3钢表面激光熔覆预置涂层,成功制备出了原位生成NbC颗粒增强的镍基复合涂层,并进行了硬度、摩擦性能测试,X射线衍射(XRD)和显微组织分析。扫描电镜(SEM)、能谱分析(EDS)和X射线衍射分析结果表明,原位生成NbC颗粒增强的镍基复合涂层与基材呈现良好的冶金结合,熔覆层的组织为先共晶析出的树枝晶(Cr,Fe碳化物相)和原位生成的NbC颗粒相均匀分布在γ(Ni Fe)基体中。硬度测试和摩擦磨损实验表明,激光熔覆原位生成NbC颗粒增强镍基复合涂层平均硬度高达HV0.31200,耐磨性是纯Ni60激光熔覆层的2.5倍。分析认为,其硬度和耐磨性提高的原因在于涂层中形成了大量的、原位生长的NbC颗粒增强相,且均匀分布于基体中。     

Preparation and characterization of biocompatible Nb-C coatings

Nb-C composite films, obtained by DC magnetron sputtering method, were investigated as possible candidates for the protective layers used in medical implants. Coatings of different carbon/niobium ratios were prepared and analyzed for elemental and phase composition, crystallographic structure, texture, corrosion behavior, and cell viability. The coating with the highest C/Nb ratio (≈ 1.9) was found to have a nanocomposite structure, in which NbC nanocrystalline phase coexists with an amorphous a-C one. The coated samples exhibited an improved corrosion resistance as compared with the Ti alloy. Cell viability measurements proved that human osteosarcoma cells are adherent to the coating surfaces, the highest viability being found for the film with the highest carbon content.     

Microstructural characteristics of PTA-overlayed NbC on pure Ti

This study uses the technique of PTA (plasma transferred arc) to overlay NbC reinforcing particles on the surface of commercially pure Ti in order to investigate the microstructural features of the overlayer and the interface between the overlayer and base metal by changing the overlaying current. The results indicate that the matrix phase of the overlayer was -Ti containing about 10 at.% Nb and 1 at.% C. NbC and precipitated TiC produced by dissolved NbC reacted with Ti dispersed in the matrix. The microstructure of the cross-section of the overlayer (from surface to base metal), which was composed of -Ti, can be separated into three layers: an upper overlayer with TiC, a middle overlayer with TiC and NbC, and a lower overlayer (interfacial layer and heat affected zone, HAZ). Due to solidification beginning at the interface and the effect of dilution, the TiC in the interfacial layer was finer. Owing to faster solidification under low-current conditions, the TiC particles were finer than under high-current conditions. Also, dendritic TiC under a low-current in the upper overlayer was also finer than under a high-current. Meanwhile, TiC precipitate that resulted from heterogeneous nucleation and Gibbs' free energy was also found around NbC. This NbC diffusion layer between TiC and NbC may have been βNb₂C phase.