高温长期时效对Hastelloy C-276合金组织和力学性能的影响

对Hastelloy C-276合金在800℃进行了不同时间的时效处理,分析了其微观组织与力学性能的变化及高温拉伸的断裂机制。结果表明:Hastelloy C-276合金在800℃长期时效后的析出相为μ相和少量的M6C相。合金时效处理150 h后,晶界处开始有析出相产生;时效170 h后,晶界处出现连续的析出相并布满了整个晶界;时效310 h后,晶粒内部开始出现析出相,晶界处开始有少量析出相沿晶界向晶粒内部生长;时效510 h后,晶粒内部有大量的析出相出现;时效超过700 h后,晶粒内部的析出相开始聚集长大,几乎布满了整个晶粒。时效处理后的合金高温拉伸的断裂机制为微孔聚集型断裂。     

晶粒尺寸对Al-Zn-Mg铝合金应力腐蚀敏感性的影响

采用慢应变速率拉伸试验、扫描电镜断口观察和透射电镜晶界微观结构观察及析出相统计等方法,研究了两种晶粒尺寸的Al-Zn-Mg铝合金在3.5%(质量分数)NaCl溶液(pH=6)中的应力腐蚀行为。结果表明:晶粒度大的Al-Zn-Mg铝合金的应力腐蚀敏感性比晶粒度小的合金要高;透射电镜的统计观察分析表明,小晶粒度小的合金的晶界析出相覆盖率高于大晶粒度合金的晶界析出相覆盖率。在一定的晶界析出相面积范围之内,析出相面积分数高的Al-Zn-Mg合金应力的腐蚀敏感性小于析出相面积分数低的Al-Zn-Mg合金。     

单晶高温合金再结晶的影响因素

研究变形量、退火温度及稀土Re元素对单晶高温合金再结晶行为的影响。结果表明:随变形量的增加,再结晶区域的面积和深度增加;低变形量下再结晶晶粒数量较少,高变形量下再结晶晶粒数量较多。退火温度影响γ’相溶解率,进而影响再结晶晶粒和晶界形貌,1270℃退火,再结晶晶粒呈枝晶状,晶界有少量M6C碳化物析出;1305℃退火,再结晶晶粒为等轴状,晶界上析出的碳化物尺寸较大、数量较多。随着Re含量的增加,合金的再结晶面积明显减小,Re元素具有抑制再结晶行为的作用。     

时效处理对GH4169合金显微组织及高温拉伸变形行为的影响

研究了在900 ℃超温服役的试验条件下,时效时间对GH4169合金的显微组织形貌、显微硬度和高温拉伸性能的影响。结果表明:随着时效时间的延长,δ相先由晶界呈短棒状析出,然后以长针状覆盖整个晶粒。时效初期晶粒有长大现象,随着δ相沿晶界的不断析出,晶粒长大现象消失。900 ℃时效处理使得GH4169合金强化相发生溶解与转化,致使合金显微硬度从44 HRC急剧降至13.6 HRC,但后续保温时间的延长对显微硬度影响较小。δ相的析出对合金的高温力学性能有显著影响,适量的析出提高了合金的抗拉强度和高温塑性,大量析出则导致合金抗拉强度变低,高温塑性变差;不同时效处理后的合金高温拉伸均为典型的弹性-均匀塑性变形,变形断裂机制皆为微孔聚集型断裂。     

Mg-Gd-Y-Zr合金的高温时效行为研究

通过金相显微镜、扫描电镜、X射线衍射等手段分析了金属型及砂型铸造Mg-Gd-Y-Zr合金高温下的时效析出行为.结果表明,经高温时效处理后,合金主要由Gd+Y在Mg中的过饱和固溶体、方块相、少量球状的Zr核及β相组成;高温时效处理几乎不影响合金的晶粒尺寸,随着时效温度的提高及高温时效时间的延长,合金的硬度逐渐降低;在晶内析出了呈三角取向或单一平行取向分布的β相,晶界上出现无沉淀析出带;成形条件并不影响高温时效析出相的分布和趋向.     

Effects of grain boundary η phase on the mechanical properties of Fe-Ni-Cr alloy

通常认为Fe-Ni—Cr合金在过时效后晶界上析出的η相为裂纹源，恶化合金性能．通过对一种Fe-Ni—Cr合金进行过时效后晶界上析出η相的研究发现，由于晶界η相与合金基体保持共格关系，η相对合金的室温性能影响不大；并且在高温变形条件下η相形成凸起，阻碍晶界滑动，减小在晶角处的应力集中，从而提高合金的高温塑性．断口扫描电镜观察表明，晶界η相的析出使合金高温断裂方式由原来的沿晶脆性断裂转变为穿晶韧窝状断裂．通过在合金中添加Nb，可以在晶界上析出更为弥散的η相，从而使得合金在高温下获得相当高的塑性．     

高温预析出后7055铝合金局部腐蚀性能和时效硬化

研究了高温预析出对Al-Zn—Mg—Cu系7055合金的应力腐蚀、晶间腐蚀和剥蚀行为以及时效硬化的影响，并通过对预析出／时效组织的透射电镜观察，阐述了预析出对7055合金各种腐蚀行为和时效硬化的影响。组织观察及腐蚀性能和力学性能测试结果表明：高温预析出处理可使7055合金抗应力腐蚀性能得到明显改善，合金应力腐蚀开裂界限应力强度因子局KISCC由7．4MPa·m^1/2提高至9．8MPa·m^1/2，合金抗拉强度仍能保持在680MPa左右。经高温预析出处理后的7055合金晶间腐蚀、剥蚀敏感性降低，7055合金的剥蚀等级由EC降为EA-。同时，高温预析出处理使晶界析出相粗化显著、离散度增大，晶界平衡析出相的Cu含量为60．18at％，且晶界析出相Cu含量提高。     

镍基材料焊接中高温失塑裂纹DDC的生成机理及研究进展

综述了镍基高温合金焊接中高温失塑裂纹(DDC)的生成及最新研究进展,讨论了镍基高温合金焊接过程中评价DDC的几种主要试验方法并着重对最适合于DDC敏感性研究的STF试验进行了详细的叙述,同时综述了高温失塑裂纹的生成机理,影响高温失塑裂纹的因素以及降低DDC敏感性的一些措施。通过综述结果表明降低DDC敏感性的主要措施是采用合适的合金体系和配合合适的焊接工艺。通过合适的合金体系来控制晶界形貌,即一些特定的元素和C形成MC类碳化物并以析出物的形式均匀分布在晶界区域内,它们会有效钉扎晶界使晶界变得更加曲折,阻碍晶界的滑移以及晶粒的长大。使用使合金组织晶粒细化的焊接工艺以及相应后续处理使合金拥有很好的抗高温失塑裂纹的性能。     

工业7N01合金的显微组织、力学性能及腐蚀性能

通过透射电子显微镜(TEM)和配备电子背散射衍射(EBSD)的扫描电子显微镜(SEM)研究晶粒形貌和析出相对两种工业7N01合金的力学性能和腐蚀行为的影响.7N01-I合金外表面再结晶度低于7N01-II合金.两种合金的强化相均为η'相.7N01-I合金的晶界析出相(GBPs)断续分布,而7N01-II合金的晶界析出相...     

GH4169合金非均匀组织在加热过程中的演化机理

通过对第二相状态、晶界取向差及晶粒尺寸演化的分析,研究了GH4169合金不均匀组织在加热过程中的演化机理.结果表明,GH4169合金中d相的体积分数在低温下随温度的升高和时间的延长而增加;在高温时随温度的升高而降低,随时间的延长先增加后降低至恒定值.第二相的钉扎作用表现为:晶内析出的d相和g"相阻碍位错的运动,沿晶界析出的d相阻碍再结晶晶粒的形核和长大,碳化物阻碍晶粒长大.小角度晶界的体积分数随加热温度的升高和时间的延长而降低;高温下,退火孪晶的生长使得小角度晶界含量增加.GH4169合金的组织演化机理主要包括:亚晶长大、再结晶晶粒的长大和退火孪晶的长大.新的再结晶晶粒主要通过亚晶长大过程获得,亚晶长大过程主要通过小角度晶界的转动和位错的迁移完成.晶粒长大过程受到抑制时,合金通过退火孪晶的形核及长大耗散其吸收的热量.     

EFFECT OF Mo AND Mo2C ON THE MICROSTRUCTURE AND PROPERTIES OF THE CERMETS BASED ON Ti（C,N）

Effect of Mo and Mo2 C on the microstructure and properties of Ti（C,N）-based cermets was investigated in this article. The results have indicated that the weight percentage of Mo from 5 to 10 can reduce Ti（C,N） grain diameter and thickness of the rim, and Ti（C,N） grain can be wetted by Ni-Cu-Mo liquid so as to get small contiguity of Ti（C,N） grain. In that way, the transverse rupture strength of Ti（C,N）-based cermets has reached 1800-1900 MPa; the fracture toughness has been due to 16-18 MPa.m1/2. But 15 wt pct Mo was not more effective on Ti（C,N）-based cermets, because the thickness of the rim becomes larger. In the circumstance of Mo2 C, 5 wt pct Mo2 C was good for microstructure and properties of Ti（C,N）-based cermets, but 11 wt pct Mo2C has resulted in larger contiguity of Ti（C,N） grain and big Ti（C,N） grain diameter so as to reduce transverse rupture strength and fracture toughness. So that, the effect of Mo on Ti（C,N）-based cermets is better than Mo2C.     

Evolution of Ti （C, N）-based cermet microstructures

Two series of Ti(C, N)-based cermet materials originating from the same chemical composition but with dif-ferent grain size distribution and sintered to different stages of the sintering cycle have been studied using SEM, TEM,EDX, and XRD. Much of the surrounding structure is formed during solid state sintering. During the solid state sintering, at first, the Mo and W rich (Ti, Mo, W)C inner rim is formed by the interaction among TiC, WC, and Mo2C; then the Mo and W lean (Ti, Mo, W)(C, N)outer rim is formed. During the liquid phase sintering, the outer rim of coarse grains grows rapidly throw a solution-reprecipitation process; aLso coarse grains grow by particle coalescence. The interface between coarse grain outer rim and binder is flat (crystal surface).     

C1023镍基高温合金中时效析出σ相

研究了5种成分的C1023镍基高温合金850 ℃时效试样中析出σ相的形态、数量、分布及其对高温持久寿命的影响.对C1023合金铸态试样进行了850 ℃保温500 h的时效热处理及850 ℃、应力325 MPa的高温持久性能测试;对时效试样显微组织和持久试样断口形貌及微区成分进行观察分析,测定了时效试样中σ相的含量.结果表明,C1023合金850 ℃时效析出的σ相有2种典型形态:在枝晶间均匀分布的颗粒以及从枝晶间伸向枝晶干的长针;在850 ℃时效240 h左右出现析出峰,时效400 h之后σ相的生成量相对稳定.存在合金成分-σ相生成量-高温持久寿命之间的良好对应关系.成分中Cr、Mo等元素含量在成分范围的下限,而C与Ti含量在成分范围中限的合金,时效σ相的生成量相对少,σ针相对短粗,对应具有相对最高的持久寿命.     

Mo对高强度钢延迟断裂行为的影响

在含V和Nb的40Cr钢中添加不同质量分数(0-1．54％)的Mo元素,采用缺口拉伸试样和改进的M—WOL型试样研究了Mo对高强度钢延迟断裂行为的影响．结果表明,随着Mo含量的增加,实验钢的延迟断裂抗力逐渐提高;当Mo含量超过1．15％时,延迟断裂抗力不再提高．EDS分析结果表明,钢中Mo元素在晶界发生偏聚,偏聚范围在几个纳米尺度内．通过电子能量损失谱(EELS)证明,Mo元素在原奥氏体晶界的偏聚能够提高钢的晶界结合强度．在钢中添加Mo能够显著提高钢的回火抗力和晶界结合强度,这是其具有高的延迟断裂抗力的主要原因．碳化物Mo2C对氢的捕集作用亦能够提高钢的延迟断裂抗力．Mo和V元素的二次硬化碳化物在半共格和非共格状态时,实验钢的延迟断裂抗力显著提高．     

掺镧TZM合金的组织结构

在TZM钼合金的基础上掺杂稀土氧化镧,用粉末冶金法生产出掺镧TZM合金。采用SEM、EDS对不同配方稀土钼合金的微观结构进行了分析。结果表明,掺镧可显著降低合金的晶粒尺寸,合金晶粒尺寸随着掺镧量的增加而减小;合金内第二相弥散颗粒不仅存在于晶界,也存在于晶内,可同时强化晶界和晶粒;间隙元素C、O会在晶界的第二相上富集,Ti在合金中会形成粗大的Ti-Mo固溶体,而C会和Mo形成粗大的Mo2C。稀土氧化镧的掺杂能促进TZM合金弥散分布的细小第二相的析出。     

Ti在bcc Fe晶界中的作用

在密度泛函理论框架下，用第一原理DMol团族方法，基于Rice-Wang热力学模型研究了合金化元素Ti对bccFe∑3[110](111)晶界结合的影响。结果表明：合金化元素Ti在晶界和自由表面的偏聚能之差为－0．372eV，Ti增强晶界结合，为韧性掺杂元素，Ti的化学效应起主要作用，贡献为－0．713eV，表现为较强的增强晶界结合作用。力学效应即掺杂引起的局域畸变贡献为 0．341eV，表现为减弱晶界结合的作用。同时分析了Ti对晶界键合的影响。当Ti原子占据晶界时，Ti使得距它较近的跨越晶界的键合加强，反映了Ti强化晶界的作用。     

DYNAMIC RECRYSTALLIZATION IN SUPERPLASTIC DEFORMATION OF TiAl BASED ALLOY

１ＩＮＴＲＯＤＵＣＴＩＯＮＳｕｐｅｒｐｌａｓｔｉｃｉｔｙｏｆＴｉＡｌｂａｓｅｄａｌｏｙｈａｓａｔｔｒａｃｔｅｄｍｏｒｅａｎｄｍｏｒｅａｔｅｎｔｉｏｎ［１－３］．Ｉｔｈａｓｂｅｅｎｆｏｕｎｄｔｈａｔ,ｄｙｎａｍｉｃｒｅｃｒｙｓｔａｌｉｚａｔｉｏｎｉｓ...     

Microstructure and Mechanical Properties of Nb- and Nb+ Ti-Stabilised 18Cr-2Mo Ferritic Stainless Steels

To explore the optimum use of stabilised elements and study the influences of stabilisation in 18 Cr-2 Mo grades,the Nb and Nb+Ti microalloying investigation focused on the relationships of the microstructure and mechanical properties of the microalloyed 18 Cr-2 Mo ferritic stainless steel thick plates.Thermo-Calc calculation was performed to predict the equilibrium phase diagrams.Afterwards,the microstructure,i.e.grain size and precipitation,of as-annealed specimens was analysed by means of optical microscopy,scanning electron microscopy and transmission electron microscopy,X-ray diffraction and energydispersive spectroscopy.Also,electron backscatter diffraction mapping was constructed to characterise grain boundary.The mechanical properties,including tensile strength and impact toughness,were tested to correlate with the microstructure.The results show that the grain sizes of Nb-stabilised steel are comparatively smaller,which is related to the fine precipitation at the grain boundaries and beneficial to the impact toughness.The increase in its strength is not apparent due to the inhomogeneous grain sizes.The grain boundary characters are similar,which is not the main factor related to their mechanical properties.When Ti is added,TiN forms above the liquidus,and large TiN particles evidently impair impact toughness.     

Influence of grain boundary composition on the moisture-induced embrittlement of Ni3(Si,Ti) alloys

Ni₃(Si,Ti) alloys containing different levels of boron were tensile tested in air at room temperature at two different strain rates. The grain boundary compositions and fracture modes of these alloys were determined by Auger spectroscopy and scanning electron microscopy, respectively. Tensile elongation and fracture mode depend upon the fabrication procedure, heat treatment, and strain rate. Widely different boron concentrations were observed at the grain boundaries, depending on the fabrication procedure and heat treatment. In addition, silicon and titanium were depleted while nickel was enriched at the grain boundaries in all specimens examined. Tensile elongations correlated well with the grain boundary concentration of boron and also with an embrittlement parameter defined as (Si+Ti−B)/Ti. A sharp brittle-ductile transition was found to occur with increasing grain boundary concentration of boron and with decreasing values of the embrittlement parameter (Si+Ti−B)/Ti. The critical grain boundary concentrations corresponding to this transition were found to be sensitive to the strain rate. All the results can be explained in terms of the effect of grain-boundary composition on moisture-induced environmental embrittlement.     

Al,Ti和Nb对Fe—Ni—Cr—Co—Nb—Ti—Al合金铸态组织的影响

对低Ａｌ,高Ｔｉ,Ｎｂ（合金Ａ）和高Ａｌ、低Ｔｉ,Ｎｂ（合金Ｂ）两种成分特征的Ｆｅ－Ｎｉ－Ｃｒ－Ｃｏ－Ｎｂ－Ｔｉ－Ａｌ合金宏观和微观铸态组织的观察分析表明,合金Ａ凝固速度较快,柱状晶区较大;两者枝晶间及铸态晶界上都分布着较多块（厚片）状富含Ｎｂ和Ｔｉ的ＭＣ和Ｌａｖｅｓ相多晶体;合金Ｂ柱状晶区晶界Ｌａｖｅｓ相较多;合金Ａ晶界ＭＣ和Ｌａｖｅｓ相附近析 体状γ′和η相及胞状η相;合金ＢＫγ′的尺寸仅约为