碳对一种单晶镍基高温合金铸态组织的影响

研究了不同碳含量对一种单晶镍基高温合金的铸态组织的影响。结果表明:随着碳含量的增加,合金的初熔温度逐渐降低,合金中的共晶数量和尺寸也减少。随着碳含量的增加,合金中的碳化物数量逐渐增多,碳化物的形态从斑点状变为斑点状和骨架状相结合的网状结构。随着碳含量的增加,一次枝晶间距变化较大,但是二次枝晶间距变化不大,W和Al元素的偏析降低,Ta和Mo元素的偏析增大。     

碳在镍基单晶高温合金中作用研究的进展

综述了碳对镍基单晶高温合金显微组织、缺陷、合金元素偏析行为、相稳定性以及拉伸性能、蠕变性能、疲劳性能等力学行为的影响及机理.总结得出,随碳含量增加,合金初熔点逐渐降低,合金中共晶数量和尺寸减少,一次碳化物逐渐增多.除W和Ta外,碳含量变化对其它合金元素的凝固偏析没有明显影响.随含碳量增大,合金蠕变寿命显著降低,最小蠕变速率增大.微量碳的添加提高疲劳寿命,屈服应力随含碳量增加而降低.比较并分析了碳对合金组织结构和力学性能的各种影响机制,并指出今后的研究方向.     

Nb含量对GH4169合金钢锭凝固及均匀化过程相演化规律的影响

以不同Nb含量的直径160 mm GH4169合金钢锭为研究对象,利用热力学软件Thermo-Calc的模拟计算及电子探针成分分析,系统研究了Nb元素含量变化对GH4169合金钢锭凝固及均匀化过程相演化规律的影响。结果表明:Nb元素含量的增加会降低合金初熔点和终熔点,扩大凝固区间,增加偏析形成的趋势;Nb元素含量的增加还可以提高GH4169合金钢锭凝固过程Laves相的析出温度,若Nb元素偏析浓度超过7.0%,Laves相的析出温度会高于标准均匀化温度1160℃,导致部分高浓度下生成的Laves相无法回溶。进一步的凝固过程中各相Gibbs自由能变化规律分析表明,GH4169合金凝固过程中,当达到Laves相的析出温度后,Laves相的形成激活能要显著小于MC碳化物,此时高浓度的Nb元素主要用于Laves相的析出和生长,Laves相的大量形成抑制了MC碳化物的进一步形成和长大,导致了Laves相与MC碳化物集合体的产生。上述的热力学分析结果与实际钢锭的相析出回溶实验结果一致。     

低Re镍基单晶高温合金平衡相析出行为的热力学模拟计算

基于Pandat热力学计算软件及Pan Ni数据库,采用热力学相平衡计算方法,研究了合金成分对低铼DD6合金平衡相析出行为的影响。结果表明:DD6合金平衡相主要为γ相、γ'相、μ相及碳化物MC和M23C6,计算结果与实验结果吻合。γ'相析出量主要由Al、Ta和Nb含量控制,随Al、Ta和Nb含量增加,γ'相析出量显著增加,固溶温度明显升高,液相初凝与终凝温度逐渐降低。C含量决定MC和M23C6的析出量,MC和M23C6析出量随C含量增加而增大。μ相析出主要受Re、W、Mo和Cr的影响,随Re、W、Mo和Cr含量增加,μ相开始析出温度显著升高,析出温度范围明显变宽,最大析出量明显增大。     

合金元素含量对K487合金组织和性能的影响

研究了Al,Ti,W,Mo,Cr合金元素含量分别在偏上限、中线、下限时K487合金的组织和性能。结果表明,合金元素含量在偏下限时,合金中析出少量的碳化物和γ′相,当提高到偏中线,碳化物和γ′相析出量增加,而提高到偏上限,碳化物和γ′相析出量进一步增加,同时析出大量针状μ相。随着合金元素含量的增加,合金的室温抗拉强度及屈服强度、750℃高温时抗拉强度及屈服强度提高;室温及高温伸长率下降,并且在合金元素含量偏上限时下降明显。综合来看,合金元素含量在偏中线时,K487合金具有较好的综合性能。     

Nb含量对GH4169合金钢锭偏析规律的影响

利用光镜、扫描电镜和能谱仪等手段分析了不同Nb元素含量的GH4169合金钢锭组织特点及元素偏析规律,并对经单阶段均匀化热处理后钢锭的组织及残留析出相特征进行分析.结果表明:随着Nb元素含量增加,GH4169合金铸锭由边缘到心部,枝晶组织粗化,二次枝晶间距增大,Nb、Ti元素的偏析系数亦增大;经1160℃保温20h的均匀化处理后,Nb添加量越多,未回溶的析出相残留越多,且残留析出相有很明显的聚集趋势,残留析出物聚合体主要为富Nb的Laves相及富Nb、Ti元素的碳化物.不同Nb元素含量钢锭中Laves相完全回溶需要的时间应不相同,在高Nb含量条件下,传统的均匀化工艺无法使Laves相完全回溶;若同时考虑钢锭的尺寸因素,高Nb含量条件下,残留析出相的聚合体可能会演化为“黑斑”缺陷而使钢锭报废.     

C对镍基单晶高温合金DD90组织的影响

研究了不同含量C对镍基单晶高温合金DD90凝固组织的影响。结果表明：随着C含量的增加,一次枝晶间距逐渐增大,凝固范围逐步扩大。随着C含量的增加,合金中碳化物数量逐渐增加。碳化物形貌从块状变为汉字体状,最后连接成复杂的骨架状。随着C含量的增加,γ/γ′共晶体积分数减少,粗大的初生相γ’减少。C的添加增大了Al的偏析,减弱了Re、Mo、W的偏析。     

Ru对一种高Cr镍基单晶高温合金凝固组织的影响

以一种新型高Cr镍基单晶高温合金为基础,调整Ru的添加量,通过对3种不同Ru含量合金铸态组织的观察,研究了Ru对合金相析出特征与元素分布规律的影响。结果表明,随着Ru含量(0、1.5%、3%,质量分数)的增加,合金一次枝晶间距与二次枝晶间距逐渐减小,(γ+γ′)共晶含量先增后降,γ′相尺寸逐渐变小;3%的Ru添加使合金凝固组织中析出β-NiAl相,该相除Ni、Al基本组成元素外,还包含一定量的Cr、Co和Ru;Ru对合金中其它元素具有典型的"逆分配"作用,β-NiAl相的析出降低了Ru对其它元素"逆分配"的影响程度;Ru提高了正偏析元素Ta、Al和负偏析元素Re的偏析程度,降低了正偏析元素Mo、Cr的偏析程度。     

B元素对DZ424定向凝固合金凝固特性及性能的影响

研究了B元素的加入对DZ424定向凝固合金凝固特性和性能的影响规律。结果表明:B元素的加入能显著降低合金的固/液相温度,加宽凝固范围,增加共晶含量;同时,由于B元素在碳化物中富集,使得碳化物形貌由草书状向块状转变。随着B含量的增加,粒状M_3B_2逐渐在共晶前沿析出;进一步增加B含量,硼化物形貌由粒状向条状转变。B的添加能够显著提高合金的持久性能,但当B添加量大于0.015%时,合金的持久性能显著降低。     

C对镍基单晶高温合金DD90凝固组织的影响

研究了不同含量C对镍基单晶高温合金DD90凝固组织的影响。结果表明:随着C含量的增加,一次枝晶间距逐渐增大,凝固范围逐步扩大。随着C含量的增加,合金中碳化物数量逐渐增加。碳化物形貌从块状变为汉字体状,最后连接成复杂的骨架状。随着C含量的增加,γ/γ′共晶体积分数减少,粗大的初生相γ′减少。C的添加增大了Al的偏析,减弱了Re、Mo、W的偏析。     

热等静压工艺对K4125镍基高温合金显微组织的影响

采用3组不同参数的热等静压(HIP)工艺对K4125镍基高温合金进行显微组织演变研究。结果表明,3种热等静压工艺制备的合金中Hf、Mo等在MC碳化物中的分布区域略有不同,Ta、Mo、Co、Cr、Ti及Al等为正偏析元素,W、Ni为负偏析元素,与其他元素相比较,Ni、Co、Cr偏析程度较小,提高热等静压温度及压力,各元素的偏析程度均有所降低,γ/γ′共晶组织含量逐渐减少,同时枝晶干γ′相的尺寸显著降低,但面积分数无明显变化。此外,3种热等静压合金均出现大块状MC碳化物碎化、二次MC碳化物析出及晶界细小碳化物形成等现象,提高热等静压温度及压力后,这种现象加剧,且碳化物中Ta、Ti含量降低,TaC、TiC的分解倾向增加。     

碳含量对热等静压态FGH96合金碳化物的影响

对不同碳含量的FGH96成型合金中碳化物进行了研究,并对合金原始粉末表面成分偏析进行了测定,以深入探讨碳含量对合金中碳化物的影响。结果表明:FGH96合金中碳含量的增加,提高了原始粉末表面碳含量和富Ti层厚度;HIP(热等静压)态FGH96中碳化物主要为富Ti和Nb的MC,随着碳含量升高,合金中分布在原始粉末颗粒边界(previous particle boundary,PPB)上和PPB以外区域的碳化物含量均逐渐升高,而非PPB碳化物含量上升的幅度相对较大;合金中碳含量越高,PPB碳化物中强碳化物形成元素的含量越低,非PPB碳化物的成分不受合金碳含量的影响;碳的加入促进了PPB碳化物的粗化,并扩展了其尺寸分布的范围;合金中碳含量越高,PPB碳化物的平均自由程越小,合金在室温下的断面收缩率越低。     

High temperature oxidation behavior of chromium‐rich alloys containing high carbides fractions. Part I: Nickel‐base alloys

Six wear‐resistant alloys based on nickel, containing 30 wt.% Cr and from 2.5 to 5.0 wt.% C, were elaborated by foundry and subjected to oxidation by air at 1000, 1100, and 1200 °C, for evaluating the oxidation behavior of hard bulk alloys. Their microstructures are rich in chromium carbides, eutectic, or pro‐eutectic, and they also contain graphite for the highest carbon contents of interest. All the studied alloys obviously display a chromia‐forming behavior, despite the initial low chromium content in the matrix. During oxidation, carbides disappear over an increasing distance from the oxidation front, with the consequence of the enrichment of the neighbor matrix in chromium. The minimal chromium content on the surface after oxidation decreases when the alloy is richer in carbon and increases with the oxidation temperature. The carbide‐free zone tends to be deeper when the oxidation temperature increases, and also when the alloy's carbon content increases, in contrast with low‐C Ni‐30Cr alloys previously studied. The disappearance of carbides means a carbon loss as gaseous oxidized species. This probably disturbs the oxide scales growing on the external surface and may influence the oxidation behavior of the alloys. When present, graphite does not deteriorate dramatically the oxidation resistance of the alloys. The hardness of the alloys are lowered by the exposures to high temperature and by the presence of graphite.     

Roles of bulk carbon content on grain size,carbide reactions and intergranular rupture life in 2.25cr martensitic heat resistant steels

The steel of a higher bulk carbon content shows the denser precipitation distribution of carbides after the solution treatment followed by tempering. Such a carbide distribution produces the smaller prior austenite grain size after the welding simulation at a high temperature. Because the equilibrium segregation concentration of phosphorus decreases with decreasing prior austenite grain size, the specimen of the higher bulk carbon content shows therefore the longer intergranular rupture life. The rupture life is also increased by the partitioning of phosphorus pre-segregated at prior austenite grain boundary/carbide interfaces onto the fresh surface of precipitates formed on the surface of pre-formed carbides. The intergranular rupture life is additionally increased by the repulsive segregation between carbon and phosphorus which decreases the overall phosphorus segregation concentration at the prior austenite grain boundaries.     

High-Temperature ductility of heat-resistant Cr-Ni alloys

Conclusions Analysis of these data leads to the conclusion that the main reason for the sharp reduction of the ductility of heta resistant nickel alloys at 1150-1250° is enrichment of boundary areas with surface-active elements (carbon in particular), the effect increasing with the extent of alloying due to the high susceptibility to grain growth of the solid solution on highly alloyed alloys. The reduction of the specific surface of grain boundaries in the coarse-grained structure increases the concentration of surface-active elements in the boundaries.This assumption is confirmed by electron fractographic data. The appearance of branced carbides in the fracture of aging nickel alloys (after slow cooling) coincides with the initial temperature of the drop in ductility and the initial solution of carbide phase and grain growth of the solid solution. With increasing alloying the branched carbides appear at lower temperatures.The appearance of branched carbides in the fractures (intergranular) must be associated not with melting of the grain boundaries but with the solution of excess carbides and the segregation of carbon in the boundaries and also with subsequent precipitaion of carbides during slow cooling. With increasing temperatures the number of branched carbides in the fracture increases and at 1200–1250° they occupy almost the entire fracture surface. This evidently points to an incrase of carbon segregation and selective propagation of cracks along grain boundaries in places where it is concentrated.However, the complex branched shape of carbides is due to the conditions of their formation in the practically two-dimentional plane of the fracture, especially since no dendrite-shaped carbides are observed in metallographic of electron microscopic analysis, i.e. branched carbides are observed only on the surface of the fracture after slow cooling.Segregation of surface-active elements, especially carbon, reduces the binding force in grain boundaries inhibits stress relaxation when crack movements along boundaries stop or slow down, and lowers surface energy at the metal-rack interface.Furthernore, the sharp grain growth of the solid solution observed at temperatures where the ductibility begins to drop leads to formation of flat boundaries at large sections, aong which crack movement is fcilitated. This facilities the process of fracture, as is indicated by the reduction of such characteristics as the work of crack initaition and work of crack propagation.     

The manufacture and characterization of WC-(Al)CoCrCuFeNi cemented carbides with nominally high entropy alloy binders

Recently, there has been increasing interest in cemented tungsten carbide hardmetals and titanium carbonitride cermets with binders of multi-component alloys (≥4 elements) or high entropy alloys (≥5 principal elements in equimolar ratios). Property improvements have been reported, such as increased ambient and elevated temperature hardness, as well as greater oxidation resistance.This study has thoroughly investigated model cemented carbides manufactured using coarse WC with a binder content of 20 wt% (32–37 vol%) from three different (Al)CoCrCuFeNi high entropy alloys (HEAs) and at different carbon levels (low, medium and high).Binder alloys were manufactured by both planetary ball milling of elemental powder mixtures and gas atomizing. Sintering was performed in vacuum for 2 h at different temperatures between 1200 °C and 1500 °C. Post-HIP treatments were also applied in some cases as all systems were difficult to densify without residual porosity.Detailed analyses were performed on the as-manufactured binder alloys, sintered binder alloys (without WC) and the actual sintered cemented carbides (WC + HEA). Various analysis methods were used to examine the materials. These included thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) to determine the melting behaviour; X-Ray Diffraction (XRD), Electron Backscatter Diffraction (EBSD) and Energy-Dispersive X-Ray Spectroscopy (EDS) to identify the type, crystal structure and exact composition of the phases present; and light optical microscopy (LOM) and scanning electron microscopy (SEM) for microstructural characterization. Additionally, the hardness and Palmqvist indentation toughness of each composition were also measured.2-Phase WC-HEA microstructures could not be obtained using the investigated high entropy alloys. Several solid solution binder alloys and numerous carbide phases were present after sintering, formed by segregation and reaction. The type and quantity of the phases depend on the carbon balance. For the compositions containing aluminium, it was found that aluminium forms oxides and intermetallic phases during sintering. The paper presents these findings in detail.     

原位观察镍基高温合金CMSX-4缩松形成过程及机理研究

采用共聚焦激光扫描显微镜(CLSM)对镍基单晶高温合金CMSX-4的凝固行为进行实时观察.并利用扫描电镜(SEM)和能谱仪(EDS)对凝固样品的微观形貌和元素偏析特性进行研究.结果 表明,在合金凝固过程中观察到缩松和碳化物的形成.缩松具有3种形态:方形缩松,五角星形缩松和角形缩松.并讨论了3种缩松的形成机理,缩松的形成...     

B元素对Fe-Cr-C系耐磨堆焊合金组织和耐磨性的影响

采用直径为1.6 mm的细径药芯焊丝,利用CO₂气体保护焊堆焊的方法制备了含有1.0%~3.0%C(质量分数),15%~20%Cr,0%~2.0%B的高铬堆焊合金.研究了B₄C含量对堆焊合金的硬度及耐磨性的影响.结果表明,堆焊合金的硬度从57.1 HRC增加到65.2 HRC,硬度提高14.2%;堆焊层合金的相对耐磨性从3.5倍提高到18.0倍.借助光学显微镜、扫描电镜和X射线衍射等微观分析方法,研究了堆焊合金的显微组织及碳化物分布形貌.结果表明,堆焊合金的显微组织主要由铁素体+奥氏体+(Fe,Cr)₇C₃组成,加入B₄C可显著改善堆焊合金层基体组织,使碳化物(Fe,Cr)₇C₃数量增加且呈弥散分布.     

Effect of additional carbon and boron alloying on the structure and mechanical properties of alloy VT22

The creation of high-strength heat-resistant alloys based on titanium is of great scientific interest. Double-phase titanium (α+β) alloys are widely used at present. The alloying sets for these alloys are mainly developed with the purpose of increasing their strength and heat resistance by solution strengthening of the phases with substitutional elements. However, the increasing strictness of the requirements on the level of their mechanical properties makes it necessary to create titanium alloys that, can be strengthened by the segregation of an intermetallic phase or chemical compounds. An important problem in the development of such alloys is the choice of the optimum composition and the attainment, of the requisite dispersity and uniformity of distribution of segregations of strengthening phases in the structure. In this connection, carbon and boron, poorly soluble in titanium and forming independent carbide and boride segregations, are of some interest as alloying additives to these alloys. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 18–22, March, 1998.