共查询到18条相似文献,搜索用时 61 毫秒
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采用现代测试技术,较详尽地研究了TiAl基合金工程材料的强韧化原理、新工艺和新技术。 在合金化方面,探讨了Sb、Pb、Sn和Nd的添加对TiAl基合金显微组织和室温力学性能的影响。其中,Sb具有显著改善 TiAl基合金室温力学性能和高温抗氧化能力的作用。TiAl+Sb合金室温变形时,α_2/γ层片状晶粒的γ板条内形成大量变形孪晶。TiAl+Sb合金的抗氧化性甚至优于Ti-48Al-2Cr-2Nb合金。 在晶粒细化剂的研究中,发现BN可使TiAl基合金铸态晶粒显著细化,其效果优于XD~(TM)技术中的TiB_2。 在TiAl基合金的表面化学热处理的开创性的探讨中,发现渗碳处理可有效地强化TiAl基合金表层,从而明显地提高合金的室温力学性能。多层、复杂结构的渗碳层具有良好的组织热稳定性和抗氧化性,因而使TiAl基合金抗高温长时间氧化能力得到显著改善。 较全面地探讨了TiAl基合金常规热加工和热处理的金属学原理,讨论了常规热处理对热变形TiAl基合金试样的局限性。在此研究基础上,提出了双温热处理新工艺。研究了双温热处理对TiAl基合金热变形试样的显微组织和室温拉伸性能的影响。探讨了双温热处理的金属学原理。 相似文献
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研究了Al含量、冷却速率和添加硼元素对TiAl合金全片层组织在1150℃的热稳定性的影响。研究表明:Al含量在46%~48%(原子分数,下同)范围的二元TiAl合金的Al含量越高,γ偏析程度越严重,铸造片层组织的热稳定性越差;Ti-48Al合金α单相区固溶处理后炉冷的粗片层组织的稳定性远远优于空冷的细片层组织,空冷细片层组织容易在晶界处发生不连续粗化转变,并且空冷片层晶粒内的魏氏片层(Lw)与基体的界面往往与晶界一同成为片层组织发生分解的起始部位;Ti-48Al合金中添加0.8%B因晶界TiB2相的存在能有效抑制细片层组织的晶界不连续粗化,但γ相从TiB2/基体界面和晶界重新形核生长可使片层组织转变为均匀的细晶近γ组织。 相似文献
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为深入揭示Ni80A镍基高温合金热塑性变形过程中晶粒细化与晶粒粗化之间的博弈关系及演进,基于晶粒细化等温变形实验和晶粒生长粗化实验分别建立了动态再结晶和晶粒生长数学模型.结合所建数学模型和有限元分析发现,Ni80A镍基高温合金在热塑性变形过程中动态再结晶晶粒细化和晶粒生长粗化的博弈关系及演进共同决定了晶粒尺寸的非线性演变.本工作绘制了两种晶粒尺寸演变机制的博弈关系图并分析其对晶粒尺寸的单独及耦合作用.结果表明:变形初期晶粒生长粗化占主导地位,变形中后期动态再结晶晶粒细化占主导地位,整个热塑性变形过程中二者相互博弈,共同影响试样的晶粒尺寸. 相似文献
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Ti-45Al-8.5Nb-W-Mo-Y合金的组织转变 总被引:4,自引:1,他引:3
研究了Ti-45Al-8.5Nb-W-Mo-Y合金的相结构。该合金铸态组织大部分由α2 γ片层域团组成,同时含有少量的B2 ω相。经过1200℃,2h处理后,B2相全部转变成ω相。合金经过70%-80%热变形后,组织由等轴γ晶粒,残余高温B2 ω相,少量的变形片层域团α2 γ片层组成。变形组织再经过1280℃,2h的热处理,其中高温相大幅度减少,同时α2板条增加。挤压态组织由变曲的片层及少量的等轴γ晶粒组成。循环热处理技术细化组织。 相似文献
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A new unstructured mesh coarsening algorithm has been developed for use in conjunction with multilevel methods. The algorithm preserves geometrical and topological features of the domain, and retains a maximal independent set of interior vertices to produce good coarse mesh quality. In anisotropic meshes, vertex selection is designed to retain the structure of the anisotropic mesh while reducing cell aspect ratio. Vertices are removed incrementally by contracting edges to zero length. Each vertex is removed by contracting the edge that maximizes the minimum sine of the dihedral angles of cells affected by the edge contraction. Rarely, a vertex slated for removal from the mesh cannot be removed; the success rate for vertex removal is typically 99.9% or more. For two‐dimensional meshes, both isotropic and anisotropic, the new approach is an unqualified success, removing all rejected vertices and producing output meshes of high quality; mesh quality degrades only when most vertices lie on the boundary. Three‐dimensional isotropic meshes are also coarsened successfully, provided that there is no difficulty distinguishing corners in the geometry from coarsely‐resolved curved surfaces; sophisticated discrete computational geometry techniques appear necessary to make that distinction. Three‐dimensional anisotropic cases are still problematic because of tight constraints on legal mesh connectivity. More work is required to either improve edge contraction choices or to develop an alternative strategy for mesh coarsening for three‐dimensional anisotropic meshes. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Abstract Grain size is an important factor affecting the mechanical properties of polycrystalline engineering materials. By conventional methods grains can be refined only by recrystallization following large amounts of plastic deformation. In the present study it will be shown how thermal cycling through the discontinuous precipitation reaction (discontinuous precipitation followed by continuous dissolution) can be utilized to obtain grain refinement in an Al‐Zn alloy without any plastic deformation. 相似文献
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Jae Hyun Jung Jaeho Choi Byoung-Soo Lee Tae-Wook Na Hyung Giun Kim 《Materials Science & Technology》2019,35(3):248-252
ABSTRACTPure titanium components fabricated by casting have a coarse grain microstructure. To improve the mechanical strength of pure titanium components by refining the grain size, the cast samples were repeatedly heat-treated. During the heat treatment, the titanium samples were repeatedly heated above the alpha-to-beta (α–β) transition temperature and cooled to room temperature to undergo phase transformation. The heating cycle was performed 1, 3, 5, and 7 times. As the number of heating cycles increased, the grain size decreased. The tensile strength was 267.9?MPa in the as-cast sample and improved to 343.4?MPa after 7 heat-treatment cycles owing to the grain size refinement, while the elongation was maintained during the heat treatment.This paper is part of a thematic issue on Titanium. 相似文献
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采用光学显微镜(OM)、电子显微镜(SEM)、能谱分析仪(EDS)、透射电子显微镜(TEM)和拉伸强度试验研究了0.3%Zr+0.2%Er和0.3%Zr+0.2%Y(质量分数)两种元素组合对Al-0.6Mg-0.9Si-0.5Cu-0.5Mn-0.2Cr合金热处理前后微观组织和力学性能的影响。研究结果表明,两种元素组合的加入均能细化铸态晶粒,其中Zr+Y改性合金的晶粒细化更明显,且两种改性合金铸态的强度和塑性均较基体合金提高。在热处理过程中,两种元素组合会影响合金中弥散相的析出,降低合金的弥散强化效果。最终,Zr+Er改性合金的强度较基体合金提高,而Zr+Y改性合金的强度则较基体降低,两种合金的塑性均较基体降低。 相似文献
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综述了钇(Y)对Mg-Al系合金的组织、室温和高温力学性能、铸造性能以及耐腐蚀性能的影响.添加适量Y不仅可以细化镁舍金的基体组织,生成高熔点强化相Al2Y,还可以改善β相(Mg17Al12)的形态,有利于铗合金室温力学性能的提高,而Y的固溶强化作用和Al2Y颗粒相的弥散强化作用既有利于室温力学性能的提高,又有利于合金高温力学性能的提高.添加适量Y也可以改善Mg-Al系合金的铸造性能和耐腐蚀性能.Y和Ce、Ca和Nd等合金元素的复合加入可有效改善镁合金的力学性能.指出了含钇Mg-Al系合金目前存在的问题,并展望了其发展前景. 相似文献