C元素含量对TiAl合金显微组织与力学性能的影响

通过XRD、SEM观察不同C含量下TiAl合金铸锭的显微组织,并对其进行硬度、抗拉强度测试。研究了C元素含量对TiAl合金显微组织与性能的影响。研究表明:未添加C元素时,TiAl合金晶粒为粗大柱状晶。当C含量为0.3at%时,柱状晶转变为等轴晶。随着C含量的增加,TiAl合金晶粒逐步细化,且层片间距逐渐减小,但并未改变γ相与α2相相间交替层片结构。C含量较少(≤0.3at%)时基体中不会出现第二相;C含量进一步增加,第二相析出明显且不断长大,富集在一起,偏析严重。TiAl合金的力学性能随着C含量增加先增强后减弱,当C含量为0.6at%时,TiAl合金的性能最佳。     

Al—Ti—C中间合金的相组成及其细化特性

用专利方法制备出各种成分的Al-Ti-C中间合金作为铝及铝合金的晶粒细化剂。对该系列中间合金的组织和物相分析表明：在制备中间合金过程中,C与Ti反应充分,生成TiC和TiAl3两种管二相,且TiAl3析出量取决于中间合金的Ti含量和Ti/C含量比。用于纯铝的晶粒细化试验表明：与Al-Ti-C中间合金相比,Al-Ti-C中间合金的晶粒细化效率更高;Al-Ti-C中间合金只有在组织中TiC与TiAl3保持适当比例时,才能对纯铝产生良好的晶粒细化效果,不含TiAl3的Al-Ti-C中间合金的晶粒细化作用很微弱;用Al-Ti-C中间合金细化纯铝晶粒时,响应时间短,但衰退较快,且不能通过熔体搅拌法予以消除。分析和探讨了Al-Ti-C中间合金的晶粒细化机理,认为“碳化物理论” 不能充分解释Al-Ti-C的晶粒细化机理,提出“Ti在TiC或TiAl3颗粒表面富集引发包晶反应”的晶粒细化机制。     

微量B,C及温度对TiAl合金热机械加工行为和显微组织的影响

研究了微量元素B和C及热加工温度对TiAl基合金的热机械加工行为及热处理显微组织的影响.结果表明,加C的合金在900-1100℃温度区间需要较大的热加工外力,而在1100-1200℃加工时,所需外应力较低.添加B能使热变形组织更加均匀,热处理后的晶粒尺寸更小,但同时也使全片层组织的片层间距增加.     

C元素对Ti-45Al-3Fe-2Mo-xC合金显微组织的影响(英文)

研究C元素对TiAl基合金(Ti-45Al-3Fe-2Mo)显微组织的影响。随着C元素含量的增加,合金中β相含量的比例降低,而片层晶团尺寸增大。当C含量增加至0.3%和0.5%时,片层间距从267 nm降低至237 nm和155nm,但是进一步增加C含量,片层间距长大至230 nm。这是由C原子的抑制作用及碳化物的析出引起的。800℃时效可以使P-型碳化物析出。随着时效时间的延长,该碳化物主要在晶界处及位错线附近析出并长大,并在不同的入射角(TEM)下有不同的形貌。对其显微组织的变化进行了详细的分析及探讨。     

Fe和B元素对Ti-46Al合金柱状晶组织的影响(英文)

对利用非自耗电弧熔炼设备得到的Ti-46Al,Ti-46Al-0.3B,Ti-46Al-0.5B,Ti-46Al-2Fe,Ti-46Al-2Fe-0.3B和Ti-46Al-2Fe-0.5B合金的凝固组织进行了研究。结果表明,铸态TiAl基合金的宏观组织为典型的柱状晶组织,而且平均柱状晶直径随着Fe和B元素的加入显著减小。其中,Ti-46Al-2Fe-0.5B合金的柱状晶直径最小。B元素可以显著地细化TiAl基合金的柱状晶组织和枝晶组织,这主要是由于B元素的添加可以显著增加固液界面前沿的成分过冷度从而细化TiAl基合金的凝固组织。而且,Fe元素的添加还可以显著地提高B元素对TiAl基合金的柱状晶组织的细化效果。     

铝硅合金晶粒细化剂Al-Ti-C-P的研制

采用自蔓延＋熔铸法制备了Al-Ti—C-P晶粒细化剂，探讨了其对共晶铝硅合金的变质效果。通过扫描电镜（SEM）、光学显微镜（OM）、能谱分析（EDS）和X射线衍射仪（XRD）等手段，研究了Al—Ti—C—P晶粒细化刺的显微组织。结果表明：Al—Ti—C—P晶粒细化剂的主要相组成为TiAl3、TiC、AlP，对共晶铝硅合金具有优良的变质效果。晶粒细化剂中的TiAl2和TiC颗粒促进了AlP时共晶铝硅合金的变质效果。     

C含量对铸造TiAl合金组织和力学性能的影响

在Ti-47.5Al-3.7(Cr,V,Zr)合金中添加0.05%~0.2%C(原子分数,下同),采用冷坩埚悬浮熔炼方法制备出了层片组织TiAl合金铸棒,通过组织观察、室温拉伸和蠕变性能测试研究了C含量对TiAl合金组织和力学性能的影响。结果表明,添加0.05%~0.2%C后,合金仍可获得择优取向层片组织。随C含量增加α2层片体积分数略有增加,层片间距呈细化趋势。当C含量超过0.1%时,在α2和γ层片内和层片界面上有细小的Ti2AlC型碳化物析出,碳化物析出相的尺寸和数量随C含量增加有所增加。添加0.05%~0.2%C后提高了合金室温的抗拉强度和屈服强度,且随C含量增加提升幅度逐渐增大,当C含量为0.2%时,分别将抗拉强度和屈服强度提升了101和123 MPa。添加C元素后显著改善了合金的蠕变性能,当C含量为0.1%时蠕变性能最佳,与不含C的合金相比,其塑性蠕变应变降低了一半、相同应变时的蠕变速率降低了1个数量级以上。添加0.1%C提升合金蠕变抗力的机制主要是通过抑制合金在蠕变初期的位错萌生和增殖过程;在γ层片中形成割阶和位错碎片阻碍位错继续运动,使得合金在蠕变第一阶段的应变硬化程度迅速增加;此外,析出的Ti2AlC型碳化物进一步强化层片界面和基体,与层片间距细化共同提高了穿层片滑移位错的运动阻力。     

Influences of Fe and B on the Columnar Structure of Ti-46Al Alloys

对利用非自耗电弧熔炼设备得到的Ti-46Al,Ti-46Al-0.3B,Ti-46Al-0.5B,Ti-46Al-2Fe,Ti-46Al-2Fe-0.3B和Ti-46Al-2Fe-0.5B合金的凝固组织进行了研究。结果表明,铸态TiAl基合金的宏观组织为典型的柱状晶组织,而且平均柱状晶直径随着Fe和B元素的加入显著减小。其中,Ti-46Al-2Fe-0.5B合金的柱状晶直径最小。B元素可以显著地细化TiAl基合金的柱状晶组织和枝晶组织,这主要是由于B元素的添加可以显著增加固液界面前沿的成分过冷度从而细化TiAl基合金的凝固组织。而且,Fe元素的添加还可以显著地提高B元素对TiAl基合金的柱状晶组织的细化效果。     

添加W对机械合金化TiAl合金显微组织和性能的影响

采用机械合金化结合粉末冶金技术制备了Ti-44．7A1-xW（at％）合金材料。采用透射电镜、扫描电镜和金相显微镜研究不同W添加量对机械合金化TiAl基合金的显微组织和高温抗氧化性能的影响，并对合金的力学性能进行测试。研究表明，通过机械合金化在TiAl基合金系统中添加微量W元素会形成新的固溶体相，这种新成分相大大提高TiAl基合金的抗弯强度σb当W添加量为1．0at％时，σb达到峰值；随后随着W含量的增加，抗弯强度降低。W元素的添加有效的制约了合金基体的内部氧化，使TiAl合金的高温抗氧化性能明显提高。     

重力铸造汽车气缸盖用AlSi7Cu3Mg二次合金的晶粒细化（英文）

研究了AlTi5B1晶粒细化和冷却速率对AlSi7Cu3Mg二次合金显微组织和力学性能的影响。采用阶梯铸模在不同冷却速率下制备添加晶粒细化剂的合金,并利用金相和图像分析技术定量研究了合金的宏观组织和显微组织。研究结果表明,添加AlTi5B1后,整个铸件具有细小均匀的晶粒组织,且在慢速凝固区域效果更显著。当冷却速率增加时,少量细化剂就可使铸件获得细小均匀组织。另外,原材料中的Ti和B以杂质的形式存在,不足以形成有效的晶粒细化效果。利用阶梯铸造法的研究结果研究了重力半固模铸造16V汽油发动机气缸盖。Weibull统计结果表明,晶粒细化改善了合金的塑形变形行为,提高了铸件的可靠性。     

加钛方式与钛含量对A356合金组织和性能的影响

研究了不同钛含量的电解A356合金的组织和力学性能,并与相应钛含量的熔配加钛A356合金进行了比较.结果表明:随着钛含量的增加,二者的晶粒和一次枝晶都明显细化,硅颗粒尺寸、纵横比均有所降低,硅颗粒圆形度有所增加,意味着硅颗粒形状得到改善.但当钛含量大于0.1%时,这种影响变弱.钛含量和加钛方式对合金的屈服强度和抗拉强度影响不大且二者相当,但塑性随着钛含量的增加而增加,当钛含量达到0.1%时,两种合金均具有最佳的塑性和质量系数.对具有相同钛含量的合金,电解加钛A356合金的晶粒和Si颗粒的尺寸小于相应钛含量熔配加钛A356合金,硅颗粒圆形度也优于相应熔配加钛A356合金,电解A356合金的塑性、质量系数均优于相应钛含量的熔配加钛A356合金,但加钛方式对硅颗粒纵横比影响不系统.     

碳和氮元素对高强度奥氏体焊缝组织和性能的影响

采用扫描电镜(SEM)和透射电镜(TEM)等分析研究了碳、氮元素对奥氏体焊条熔敷金属组织和性能的影响.结果表明,随着碳含量的增加,熔敷金属晶界上M23C6碳化物析出物逐渐增多,析出颗粒增大,虽然熔敷金属的抗拉强度有所提高,但韧性明显降低,碳含量增加到一定程度后,对强度的影响趋于平缓,但对晶界碳化物的数量和尺寸仍然有强烈的促进作用,韧性持续降低,耐晶间腐蚀性能大大降低.随着氮含量的增加,抗拉强度呈持续上升趋势,同时韧性仍能保持在较高水平,晶界上析出碳化物少,抗晶间腐蚀性能良好.     

Experimental and simulation studies on grain growth in TiC and WC-based cermets during liquid phase sintering

The grain growth behaviors of TiC and WC particles in TiC-Ni, TiC-Mo₂C-Ni, WC-Co and WC-VC-Co alloys during liquid phase sintering were investigated for different Ni or Co contents and compared with the results of Monte Carlo simulations. In the experimental study, TiC-Ni and WC-Co alloys had a maximum grain size at a certain liquid volume fraction, while the grain size in TiC-Mo₂C-Ni and WC-VC-Co alloys increased monotonically with an increasing liquid volume fraction. These results mean that the grain growth of these alloys cannot be explained by the conventional mechanisms for Ostwald ripening, namely diffusion or reaction controlled processes. Monte Carlo simulations with different energy relationships between solidliquid interfaces predicted the effect of the liquid volume fraction on grain size similar to the experimental results. The contiguous boundaries between solid (carbide) particles appear to influence the grain growth behavior in TiC- and WC-based alloys during liquid phase sintering.     

Microstructural effects on the high temperature oxidation of two-phase Cu-Cr alloys in 1 atm O2

The oxidation of a Cu-Cr alloy containing about 60 wt% Cr and of two Cu-Cr alloys containing about 40 wt% Cr was studied at 700 and 800 °C in 1 atm O₂. The 60 wt% Cr alloy was prepared by powder metallurgy (PM) and had a phase particle size of 50-150 μm. One of the two alloys containing about 40 wt% Cr was prepared by mechanical alloying (MA) and had a phase grain size ranging from 10-50 nm to 200-300 nm, depending on the location, while the other was prepared by magnetron sputtering (MS) and had a phase grain size around 5-10 nm. The most important difference between the oxidation behavior of the three alloys is the formation of an exclusive chromia scale on the surface of the Cu-40 wt% Cr alloy prepared by magnetron sputtering and of a continuous chromia layer beneath an outermost layer of copper oxides on the corresponding alloy prepared by mechanical alloying, while the Cu-60 wt% Cr alloy prepared by powder metallurgy formed complex scales composed mostly of CuO, Cu₂O with some Cu₂Cr₂O₄ and Cr₂O₃. Thus, the microstructure of two-phase binary alloys has a strong effect of their oxidation behavior. In particular, a decrease of the alloy grain size favors the exclusive external oxidation of the most reactive component, reducing the corresponding critical content in the alloy. This effect is attributed to the presence of larger concentrations of rapid diffusion paths for the migration of the components in the alloy as well as to a faster dissolution of the particles of the Cr-rich phase in the copper matrix.     

Effect of additional elements on aging behavior of Al-Zn-Mg-Cu alloys by spray forming

1 Introduction Spray atomization and deposition technology, also termed spray forming, has attracted considerable attention because of its excellent potential advantages in the production of structure materials: cost-effectiveness in combination with pro…     

Nb含量对机械合金化Cu-Nb合金晶粒细化和力学性能的影响

采用机械合金化法制备了Cu-xNb(x=0-30%)合金粉末,通过X射线衍射仪(XRD)、金相显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)观察和显微硬度测量分析了Nb溶质含量对粉末晶粒细化过程以及力学性能的影响。结果表明,尽管Nb与Cu的平衡固溶度接近为0,经100h球磨后,Nb在Cu中的最大固溶量可达约11wt%。随着Nb含量的增加,Cu-Nb合金粉末的晶粒细化能力提高。这是由于随着偏析至位错处的溶质原子数量增加,合金的回复过程得到抑制,因此有利于晶粒尺寸的减小。Cu-30wt%Nb合金球磨100h后Cu相平均晶粒尺寸减小至约6nm。此外,球磨Cu-Nb合金粉末的显微硬度随着Nb含量的增加而提高,其强化机制主要为细晶强化和固溶强化。     

纳米硬质合金制备技术的研究

研究了 WC-Co纳米硬质合金的制备技术。采用强化球磨、添加晶粒长大抑制剂和低温加压烧结工艺 ,获得了 WC晶粒度接近 2 0 0 nm的硬质合金。研究了 VC和Cr3 C2 两种抑制剂加入量对合金组织、WC晶粒度和性能的影响以及抑制晶粒长大的机理。研究结果表明 ,添加 VC和 Cr3 C2 晶粒长大抑制剂十分有效的抑制了晶粒的长大 ,合金中的 WC晶粒度随抑制剂加入量的增加而细化。但过多的抑制剂不仅会导致碳化物在 WC/Co晶界上大量析出 ,而且也会增加孔隙度 ,结果增加了合金脆性 ,降低了合金的强度 ,其有害影响 VC比 Cr3 C2 更大。采用加压烧结可消除合金中的孔隙提高合金的强度。     

Microstructure and properties of high chromium cast irons: effect of heat treatments and alloying additions

Abstract

Different combinations of critical and subcritical heat treatments variously modify the initial as cast microstructure of high chromium white cast irons leading to secondary carbide precipitation of different extent and nature. Destabilisation (critical heat treatment) of austenite at 970°C for 2·5 h followed by annealing (subcritical heat treatment) at 600°C for 13 h results in massive precipitation of M₂₃C₆ carbide particles along with spheroidised M₇C₃. The reversed order of heat treatments leads to extensive precipitation of M₇C₃ secondary carbide particles. Mo has a favouring effect on the hardness of the microstructures containing pearlite by limiting pearlite formation. The gradual increase in the alloying additions, C and Cr, increases the hardness of the materials at the different treatment states by inducing carbide precipitation. The increase in the Si content leads to the opposite effect by favouring pearlite formation.     

Effect of Al5Ti1B master alloy on microstructures and properties of AZ61 alloys

AZ61 alloys with different levels of Al5Ti1B master alloy additions were prepared by conventional casting method.The effects of Al5Ti1B contents and holding time on microstructures and microhardness of AZ61 alloys were studied by XRD,OM and microhardness testing techniques.The results show that when the addition level of Al5Ti1B master alloy is less than 0.5%(mass fraction),the average grain size of the alloys decreases with the increase of Al5Ti1B content at the same holding time.But the grain size increases somewhat with further addition of Al5Ti1B.The average grain size of the alloys decreases with the increase of the holding time as it is less than 30 min at the same addition level of Al5Ti1B.It is considered that TiB2 particles can serve as the heterogeneous nucleation sites ofα-Mg during solidification,and heterogeneous nucleation is the main reason for the grain refinement of AZ61 alloys.The microhardness of the refined AZ61 alloys with 1.0%Al5Ti1B addition is increased by about 8%.     

Zn含量对反挤压Mg-8Sn-Zn合金组织演变和力学性能的影响

利用OM,SEM,TEM,EBSD,XRD和电子材料试验机研究了Zn含量（1%-4%,质量分数）对反挤压Mg-8Sn-Zn合金组织、织构演化和力学性能的影响.结果表明,所有合金均可在相对较低的挤压温度（250℃）和较高的挤压速度（2 m/min）下成形.在反挤压过程中,所有在均质化处理后残留的粗大第二相在挤压过程中破碎并沿着挤压方向被拉伸成条带状;所有的粗大晶粒均转变为细小的等轴晶,其平均晶粒尺寸分别为7.4,8.3和10.5μm.随着Zn含量的增加,在挤压态合金晶内和晶间分布的细小弥散第二相的体积分数增加,这些第二相主要由亚微米级的Mg₂Sn相和纳米级的富Zn相组成.弥散分布在晶界上的第二相有效地钉扎了晶界,从而细化了晶粒尺寸.另外随着Zn含量的增加,合金的织构强度降低,这和变形晶粒的体积分数减小有关.组织细化、织构弱化和第二相弥散化是Mg-Sn-Zn合金强度提高和拉伸/压缩屈服点各向异性减弱的主要因素.