定向凝固超高强度NiTi基自生复合材料

在NiTi合金中添加少量Al、Nb、Hf强化元素, 采用定向凝固原位自生法制备了一种NiTi基自生复合材料, 并在950 ℃对定向凝固棒分别进行了12 h、50 h及100 h的均匀化热处理, 对热处理后的试样进行了室温抗拉强度测试。结果表明, 定向凝固组织为沿[001]方向生长的细小的棒状胞晶组织, β-Nb相和Ti₂Ni相增强体颗粒沿NiTi胞晶间的[001]方向排列。随热处理时间的延长, 胞晶尺寸逐渐粗化, 两增强相粒子分布更加弥散均匀。热处理后NiTi基自生复合材料的最大抗拉强度达到1972 MPa, 超过了4130和8640超高强度钢, 与4140和4340超高强度钢的强度基本相当, 达到或超过了多种国内外现役的超高强度钛合金。     

凝固工艺对自生复合Cu-Cr合金电车线综合性能的影响

自生复合Cu-Cr合金是一种高强度与高导电率兼顾的新型电车线材料。本文采用定向凝固连续铸造技术成功制备了纤维增强的自生复合Cu-Cr合金电车线线坯,考察了合金成分、定向凝固连铸的工艺参数对电车线的力学性能、导电性能及综合性能M指标的影响。     

Ni,Cr,Al—TaC自生复合材料的定向凝固组织特性

本文采用高梯度定向凝固装置制备Ni-TaC共晶自生复合材料。系统地研究了凝固速率对凝固组织的影响。随凝固速率增大,固液界面依次呈现平一胞一枝的形貌。TaC纤维增强相的平均间距和截面积随凝固速率增大而减小,其体积分数可在一定范围内调节。与此同时,随凝固速率的增大,γ′相形貌趋于规整,尺寸减小。     

Ni,Cr,Al-TaC自生复合材料的定向凝固组织特性

本文采用高梯度定向凝固装置制备Ni TaC共晶自生复合材料。系统地研究了凝固速率对凝固组织的影响。随凝固速率增大 ,固液界面依次呈现平一胞一枝的形貌。TaC纤维增强相的平均间距和截面积随凝固速率增大而减小 ,其体积分数可在一定范围内调节。与此同时 ,随凝固速率的增大 ,γ′相形貌趋于规整 ,尺寸减小。     

定向凝固Cu-Cr自生复合材料显微组织和力学、电学性能研究

运用Bridgman技术制备Cu-Cr自生复合材料,研究了凝固方法和凝固速率对凝固组织及性能的影响,分析了复合材料性能提高的原因.结果表明:复合材料的组织是由α基体相和分布于α相间的纤维状共晶体复合组成,随凝固速率增加,各组织生长定向性变好且径向尺寸均得到细化;致密、均匀、规整排列的组织减少了横向晶界,而复合材料的断裂受共晶增强体的断裂控制,使得复合材料的强度、塑性、导电性均高于体积凝固试样,使复合材料的综合性能提高.     

定向凝固Cu-Cr自生复合材料的拉伸性能和断口形貌特征

研究了Cu-Cr自生复合材料定向凝固试样的轴向拉伸性能和拉伸断裂机制,探讨了凝固速率对性能及断口形貌的影响.结果表明: Cu-Cr自生复合材料具有良好的常温拉伸性能,随着凝固速率增加,材料的轴向拉伸强度呈上升趋势.断口形貌观察表明:复合材料中的纤维状共晶体(α β)是应力的主要承载体,共晶体的断裂是Cu-Cr自生复合材料断裂的控制机制.     

自生复合Cu-0.8Cr合金定向凝固过程研究

研究了非平衡状态下Ｃｒ－０．８ｗｔ％Ｃｒ亚共晶合金的定向凝固过程。结果表明,当温度梯度为３０℃／ｃｍ,生长速度分别为３μｍ／ｓ和３０μｍ／ｓ时,Ｃｕ－０．８ｗｔ％Ｃｒ合金的非平衡凝固组织;当温度梯度为３０℃／ｃｍ时,α枝晶一次间距随生长速度的增大而增大,这与枝晶一次间跨的Ｈｕｎｔ模型在低束祺段的规律一致,而与Ｋ－Ｐ模型的规律相反;Ｃｒ纤维的形成主要与液态Ｃｒ表面张力,Ｃｒ原子在液相中横向扩散能力及     

自生复合Cu08Cr合金定向凝固过程研究

研究了非平衡状态下Ｃｕ０８ｗｔ％ Ｃｒ 亚共晶合金的定向凝固过程。结果表明, 当温度梯度为３０℃／ｃｍ , 生长速度分别为３μｍ ／ｓ 和３０μｍ ／ｓ 时, Ｃｕ０８ｗ ｔ％ Ｃｒ 合金呈（α枝晶＋ 共晶） 的非平衡凝固组织; 当温度梯度为３０℃／ｃｍ 时, α枝晶一次间距随生长速度的增大而增大, 这与枝晶一次间距的Ｈｕｎｔ模型在低速度段的规律一致, 而与ＫＰ模型的规律相反; Ｃｒ 纤维的形成主要与液态Ｃｒ 的表面张力、Ｃｒ 原子在液相中横向扩散能力及α枝晶间Ｃｒ 相的生长环境有关,增强Ｃｒ 原子的扩散能力,减小α枝晶侧向分枝及其间隙尺寸有助于规则Ｃｒ纤维的形成。     

自生复合材料及其进展

自生复合材料由于其相与相之间无润湿、化学反应等问题,因此其有独特的优点。本文简要介绍了自生复合材料的理论、制备及研究现状和展望。     

高温共晶自生复合材料的研究进展

介绍了高温共晶自生复合材料的应用潜力，分析了自生复合材料的研究热点，指出了自生复合材料发展中存在的问题。     

Cu-15Cr-0.1Zr原位复合材料中纤维相的组织演变

通过感应熔炼、铸造、锻造和冷拔变形制备了Cu-15Cr-0.1Zr原位复合材料.采用SEM和TEM观察分析纤维相组织形态的演变.在较低的应变量下纤维保持着与铸态树枝晶相同的bcc单晶结构,在较高的应变量下,单根Cr纤维被分隔为一些由亚晶界组成的亚结构,相邻亚晶的偏差角在5～30°之间.     

Microstructure evolution of directionally solidified Nb–Si alloy

Abstract

By taking the method of liquid–metal cooled directional solidification, alloys with a nominal composition of Nb–14Si–24Ti–10Cr–2Al–2Hf (at-%) were prepared under different conditions. Alloys were initially directional solidified with different withdrawal rates (R?=?1·2, 6, 18 mm min^?1) at 1750°C and subsequently heat treated at 1450°C for 10 h. These processes aimed to investigate the microstructure of directionally solidified (DS) and heat treated (HT) alloys by XRD, SEM, and EDS. The microstructure of DS alloy was composed of (Nb,Ti)_SS, (Nb,Ti)₅Si₃, and Laves phase Cr₂Nb, and the former two components formed (Nb,Ti)_SS+(Nb,Ti)₅Si₃ eutectics. In addition, (Nb,Ti)₅Si₃ laths only presented in DS1·2 alloy. With the increasing withdrawal rates, the microstructure of alloy altered from hypereutectic into pseudo-eutectic, accompanied with the eutectic morphology transformation from petaloid into coupled. Also, the dimension of constituent phases reduced. However, after heat treatment, the constituent phases did not change. The petaloid morphology of eutectics in DS specimens disappeared and coupled eutectic transferred into network. The block or needle-like Cr₂Nb gathered along the boundary between (Nb,Ti)₅Si₃ and (Nb,Ti)_SS, and the overall alloy composition became homogenisation.     

Microstructures and fracture toughness of directionally solidified Mo-ZrC eutectic composites

Microstructures and fracture toughness of arc-melted and directionally solidified Mo–ZrC eutectic composites were investigated in this study. Two kinds of directionally solidified composites were prepared by spot-melting and floating zone-melting. Microstructure of the arc-melted composite (AMC) consists of equiaxed eutectic colonies, in which ZrC particles are dispersed. The spot-melted composite (SMC) exhibits spheroidal colony structure, which is rather inhomogeneous in size and morphology. ZrC fibers in the eutectic colonies are aligned almost parallel to the growth direction. Well aligned, homogeneous columnar structure with thin ZrC fibers evolves in the floating zone-melted composite (FZC). Texture measurement by X-ray diffractometry revealed that the growth direction of Mo solid solution (Mo_SS) in FZC is preferentially 〈100〉, while that of SMC is scattered. Fracture toughness K_q evaluated by three point bending test using the single edge notched beam method is >13 MPa m^1/2 for AMC, 20 MPa m^1/2 for SMC and 9 MPa m^1/2 for FZC. Intergranular fracture along colony boundaries is often observed in AMC. In contrast, transgranular fracture is dominant in SMC and FZC, although significant gaps caused by intergranular fracture are occasionally observed in SEM micrographs of SMC. Fracture surface in FZC is wholly flat. Pull-out of ZrC occurs owing to Mo/ZrC interfacial debonding in intergranularly fractured regions of AMC and SMC.

Coarse elongated colonies in SMC and FZC induce transgranular fracture instead of intergranular fracture. Intergranular fracture and interfacial debonding in AMC and SMC causes frequent crack deflection accompanied by ligament formation and crack branching, which is responsible for the high fracture toughness of the composites. Preferred 〈100〉 growth of Mo_SS phase in FZC leads to brittle 〈100〉 cleavage fracture associated with low fracture toughness.     

定向凝固A1-Bi偏晶合金中第二相的粗化行为

为了获得第二相弥散分布的偏晶合金,在定向凝固条件下,对Al-Bi偏晶合金的凝固行为进行了研究,考察了第二相体积分数对凝固组织的影响,并对第二相粒子的粗化因素进行了分析.研究结果表明:用定向凝固方法可以制得具有弥散第二相分布的偏晶系Al-Bi合金;在一定的生长条件下,第二相粒子的半径随体积分数的增大而增大;第二相体积分数以及熔体中存在的Stokes流和Marangoni对流是引起第二相粒子粗化的主要因素.     

定向凝固Fe-6.5wt%Si合金热压缩变形行为研究

采用Gleeble 1500热模拟机对定向凝固Fe-6.5%(质量分数)Si合金进行热压缩变形研究。结果表明,Fe-6.5%(质量分数)Si合金柱状晶组织热形变过程中很难发生动态再结晶,以动态回复为主,易产生严重的变形带;在无序相区间,在柱状晶晶界处发生动态再结晶形核,但长大受到限制,仅局限于晶界附近。与锻态等轴晶组织相比,有序相区间,两种组织形变行为基本一致,受温度影响剧烈,在无序相区间,随温度升高,等轴晶组织的形变激活能略有升高,平均值约为294kJ/mol,而柱状晶组织的形变激活能逐渐降低,平均值约为260kJ/mol。     

Microstructures of directionally frozenin situ composites of multicomponent eutectics

Microstructural variations of binary (Sn-Pb, Sn-Cd, Pb-Cd), ternary (Sn-Pb-Cd) and quaternary (Sn-Pb-Cd-Zn) eutectics which were permitted to solidify directionally were investigated in terms of the controlled solidification rates. It was found that, at an appropriate freezing rate, the structure was lamellar and satisfied the Jackson-Hunt relationship, and furthermore, that the order of the layers present in the solidified eutectics was definite, such that in the case of Sn-Pb-Cd ternary eutectic alloy, for instance, the Sn-Cd layers would not be allowed to be in contact. An explanation for this could be the high interfacial energy between the two. The authors would like to express their sincere appreciation to Mita Industries Co., Ltd. for financial support in this investigation.