用正电子湮没技术研究Zr对Ni3Al缺陷态的影响

本文用正电子湮没技术（ＰＴＡ）研究了含不同Ｚｒ量多晶Ｎｉ３Ａｌ的ｅ＾＋寿命谱，结果表明：在Ｎｉ３Ａｌ中加入Ｚｒ，一部分Ｚｒ原子进行原子替位，晶格发生畸变，导致基体中正电子寿命（τ１）增长；另一部分在晶界偏聚的Ｚｒ调整了晶界结构，使平均寿命（τ）下降，当Ｚｒ量为１．２ａｔ－５时，缺陷态的寿命τ２显著增长，表明有自由体积较大的缺陷组态生成。     

硼在金属间化合物Ni3Al晶界的平衡偏聚

应用扫描俄歇探针研究了硼在金属间化合物Ｎｉ３Ａｌ晶界的平衡偏聚特性。研究结果表明，硼在Ｎｉ３Ａｌ晶界的偏聚符合Ｌａｎｇｒｎｕｉｒ一ＭｃＬｅａｎ平衡偏聚理论；实验得到硼在Ｎｉ－２４ａｔ．－％Ａｌ合金中晶界偏聚自由能△Ｇ＝－２２１５９－２４．７４Ｔ（Ｊ／ｍｏｌ）：硼在Ｎｉ３Ａｌ晶界的偏聚受晶界结构和晶界化学环境的影响。不同结构的晶界存在着硼偏聚的不均匀性，硼在富镍晶界的偏聚比在富Ａｌ晶界更为显著，合金元素对硼在Ｎｉ３Ａｌ晶界偏聚的影响与其在Ｎｉ３Ａｌ中占据的亚阵位置有关。     

Ni3Al晶界结构的计算机模拟

本文运用嵌入原子法势函数和静态弛豫最陡梯度的计算方法,模拟[100],[110]和[111]轴一系列具有不同晶界几何参量及化学成分的Ni_3Al对称倾侧晶界原子结构、晶界能和晶界的内聚能、电荷密度分布及应力场等内容,并着重研究和讨论了它们与硼偏聚,Ni_3Al的晶界韧脆行为,特别是硼韧化的化学计量效应之间的关系。     

铸造Ni3Al基合金的韧化研究

本文报道了铝当量为19-23at.-%的一系列铸造Ni_3Al基合金的显微组织和塑性及其与合金元素间关系的研究结果。表明,Hf、Ti和Zr显著地改变初生Ni_3Al(γ’)相的形态和分布并细化其尺寸,而Nb、W和Ta则不具有上述作用,在显微组织被细化的合金中,形成韧性的γ’-γ-γ’界面,消除了本质弱化的γ’-γ’脆性界面,初生相的尺寸可以控制在几十微米,表现出良好的塑性,尤其是中温塑性有较大改善。另外,组织细化的合金在无Cr时仍有可观的塑性,Cr对改善中温塑性有益,这可能是由于它改变合金中的γ相的数量和分布的结果。     

Ni3Al中B和Mg的非平衡晶界共偏聚

在1023－1373K的初始温度和0.05-268.91K/s的冷速范围内，用Auger剖层分析确定含B和Mg的Ni3Al合金中B和Mg的非平衡晶界共偏聚行为，按照溶质－空位复合体迁移机制所导出的描述非平衡晶界偏聚的扩散速率方程解析表达式，很好地模拟了本实验结果，并确定了Ni3Al-B-Mg合金中B及B－空位复合体，Mg及Mg-空位复合体的扩散系数及复合体激活能。     

Ni3Al中Al含量对硼韧化作用的影响

本文利用“有序—无序”模型对Ni_3Al中的点阵空位与成分的关系进行了计算,结果证明,当Al含量超过化学计量值时,Ni_2Al中有大量的点阵空位存在,称之非化学计量空位。正电子湮没技术证实了这种空位的存在。由此解释了Al含量对硼韧化作用的影响。     

两种含硼Ni3Al合金的微观组织与力学性能

本文研究了两种不同硼含量Ｎｉ３Ａｌ合金的微观组织、室温拉伸及高周疲劳性能，Ｎｉ３Ａｌ（０．６ａｔ．－％Ｂ）合金为单相组织，Ｎｉ３Ａｌ（１．０ａｔ．－％Ｂ）合金中除γ相外，还有微量共晶体，虽然Ｎｉ３Ａｌ（１．０Ｂ）的拉伸强度较Ｎｉ３Ａｌ（０．６Ｂ）的高，但在相同的循环应力水平下，后者的疲劳寿命显著高于前者的，疲劳断口观察表明两种合金的疲劳裂纹萌生和扩展行为各不相同。     

Li对Ni3Al力学性能的影响

本文研究了含微量Ｌｉ的Ｎｉ３Ａｌ合金力学性能，结果发现Ｌｉ能提高Ｎｉ３Ａｌ的屈服强度，适量Ｌｉ能改善Ｎｉ３Ａｌ室温塑性，其断口形貌由Ｎｉ３Ａｌ合金的沿晶断裂变为混晶断裂；但Ｌｉ不能改善Ｎｉ３Ａｌ合金的中温脆性，对Ｎｉ３Ａｌ＋Ｂ合金室温塑性影响也不大。ＸＰＳ研究表明，Ｌｉ偏聚于Ｎｉ３Ａｌ合金晶界。本文给出了Ｌｉ提高多晶Ｎｉ３Ａｌ塑性的初步解释。     

EFFECT OF Zr,Cr AND B ADDITIVES ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Ni_3Al ALLOYS

The microstructure and the mechanical properties from room temperature up to 1050℃ ofNi_3Al alloys containing 0—0.6 at.-%Zr,0—7.7 at.-%Cr and 0—2.22 at.-%B have beenstudied.It was found that the temperature dependence of their yield strength variation revealsto be anomalous,i.e.the strength increases with the temperature raising,and then decreasestill it surpassed the peak value.Both Zr and Zr+Cr may improve the yield strength of the al-loys in the entire range of testing temperatures,as well as the tensile strength and elongationunder high temperatures.B is favourable to raise the tensile and yield strengths of the alloys,and also plasticity.But the strength will reduce as B added is over 2.22 at.-%.TheNi_(20)Al_3B_6 and Ni_3Al eutectic mixture like islands and globes precipitated inside the grainsand along the grain bounderies,which are harmful to the strength and ductility,may beformed when the B content exceeds the limit of solubility.     

Zr,Cr和B对Ni3Al合金组织和力学性能的影响

本文研究了含Zr(0—0.6at.-％),Cr(0—7.7at.-％)和B(0—2.22at.-％)的Ni_3Al合金的组织和室温至1050℃拉伸性能。结果表明,Ni_3Al合金的屈服强度随温度升高而增加,表现出反常的温度关系。到达峰值后,随温度升高,屈服强度降低。Zr和Zr+Cr在整个试验温度范围都增加Ni_3Al合金的屈服强度,并改善高温抗张强度和塑性。硼增加Ni_3Al合金的抗张强度和屈服强度,同时改善塑性。但当硼含量超过1.37at.-％时,则降低强度和塑性。当硼含量超过溶解度极限时,Ni_3Al合金中形成岛状和球状的Ni_(20)Al_3B_6和Ni_3Al的共晶组织,对强度和塑性都是有害的。     

CERIUM-INDUCED GRAIN BOUNDARY STRENGTHENING OF Ni_3Al ALLOYS

1.IntroductionSincel979,agreatdealofresearch{1-5]hasbeendirectedtowardshowtoimprovetheductilityofintermetalliccompoundNi3AIbecauseofitsspecialproperties.ThisaluminidewithanL12orderedcrystalstructurebelowtheperitectictemperature(1395"C)[']hasgoodhigh-temperaturepropertiesl2l5]andcorrosion.esista.ce[7].However,themainprob1emfOrNisAlasahigh-temperaturestrllcturalmaterialisitslowductilitvandbrittlenesswhenitisinthepolycrystallinefo.m[8].Thisbrittlenesseffectivelyhindersitsfabricationintousefll…     

COMPUTER SIMULATION OF GRAIN BOUNDARY STRUCTURES IN Ni_3Al

The embedded atom type potentials and static relaxation method combined with steepest gra-dient computational technique have been used to simulate the grain boundary cohesive ener-gies,the distribution of electron density and stress field in the grain boundary,region,and oth-er related problems of[100],[110]and[111]symmetric tilt grain boundaries in Ni_3Al withdifferent grain boundary geometrical index and composition.Their relations with the segrega-tion or boron,behaviors or the grain boundary,and especially the stoichiometrical effect of Binduced ductility have also been studied and discussed.     

Si对过共析锰钢力学性能及晶界组织的影响

本文用ＳＥＭ、ＴＥＭ研究了Ｓｉ对过共析锰钢经９５０℃奥氏体化和５６０℃等温处理后的组织及力学性能的影响。结果表明，Ｓｉ提高冲击韧性和延伸率，抑制先共析渗碳体在奥氏体晶界呈连续网状析出，并促进在过共析钢中晶界铁素体的形成，本文重点讨论了含Ｓｉ过共析钢中晶界铁素体的形成机理及其对韧性的影响。     

SLIP FEATURE AND GRAIN BOUNDARY BEHAVIOURS OF Ni_3Al ALLOYS DURING DEFORMATION

The deformation behaviours of Ni_3Al alloys with various chemical compositions and subjectedto different heat treatments were in situ observed under SEM. Moreover,in situ observationsof slip trace were supplemented by the direct observation of dislocation arrangements underTEM.In B-doped Ni_3Al alloys it is shown that close to the grain boundary there exists a thinslip transition region,within which slip lines are reoriented or other slip systems are operatedto produce a local strain accommodation and to relax the stress concentration at grain bound-aries.Boron seems to lower the stress for dislocation generation from the grain boundaries orto ease the cross-slip close to the boundaries,and also to increase the number of dislocationsources.However,B-enhenced ductility is seriously affected by stoichiometry,the addition ofa tertiary alloy element and heat treatment,etc..     

Ni3Al合金的滑移特征及形变过程的晶界行为

通过SEM动态拉伸形变试验,研究了具有各种化学成分和不同热处理态Ni_3Al合金的形变滑移特征,并用TEM观察了晶界区域的位错组态。研究结果表明,在含硼Ni_3Al合金的晶界附近存在一个过渡滑移区,该区域中滑移线重新取向或其它滑移系开动,从而产生了局部应变调节并使晶界应力集中松弛。硼降低了开动晶界位错源所需的应力并可能同时增加了位错源本身的数目。硼对Ni_3Al的韧化作用强烈受到基体Al含量、合金元素及热处理等因素的影响。