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室温拉伸塑性是TiAl合金这类低损伤容限材料工程化应用必须考虑的重要指标之一。高温热暴露后TiAl合金的室温塑性显著降低,这不利于TiAl合金部件的应用可靠性。概述了高温热暴露对TiAl合金室温拉伸性能特别是室温拉伸塑性的影响,重点归纳了高温热暴露造成的表面性质变化对该合金室温塑性不利影响的可能机制,并提出了抑制热暴露所致室温塑性降低的可能途径。分析表明,热暴露导致TiAl合金室温拉伸塑性降低,是表面氧化致脆、表面残余应力以及环境潮气等因素综合作用的结果,其中表面氧化致脆是直接原因。改善基体的抗氧化性或者形成可抑制表面裂纹向基体扩展的有利组织,是保持TiAl合金高温使用后室温拉塑性水平的有效途径。 相似文献
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显微组织应变率对全片层TiAl合金室温塑性的影响 总被引:2,自引:0,他引:2
采用了特殊的热处理工艺,分别获得了不同晶粒度和不同片层厚度的显微组织的全片层TiAl合金,并在不同的应变速率下,对这些合金进行了室温单向拉伸实验.结果表明:在一定的应变速率下,晶粒度的降低和片层厚度的增加都会导致全片层TiAl合金室温塑性的增加.在确定的显微组织下,应变率的降低,会导致全片层TiAl合金室温塑性的增加.而当应变率较低、晶粒较大、片层较厚时,试样中容易萌生微裂纹.微裂纹多数在软取向的晶粒中出现.具有小晶粒、厚片层显微组织的全片层TiAl合金在较低的应变速率下将会具有较好的塑性. 相似文献
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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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以包套挤压镍微合金化TiAl合金为研究对象,研究了热处理工艺对合金组织和室温、800℃拉伸性能的影响.结果表明,70%变形量包套挤压合金经(α γ)双相区1250℃热处理获得了再结晶完全的双态组织,其中不含有残留的层片结构;挤压合金经(α2 γ)双相区退火处理后,合金室温拉伸屈服强度为535MPa,抗拉强度为650MPa,延伸率为3%;800℃拉伸屈服强度为365MPa,抗拉强度为400MPa,延伸率为156%,这种组织有利于进一步加工成形,使超塑成形成为可能. 相似文献
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TiAl基合金冷坩埚定向凝固研究现状与发展趋势 总被引:1,自引:0,他引:1
冷坩埚定向凝固技术基于材料电磁加工原理,将合金连续熔化、电磁约束成形和连续凝固过程统一,避免模壳法定向凝固造成的合金熔体污染,是TiAl等高活性合金高纯净定向凝固的重要方法之一。报告了TiAl基合金冷坩埚定向凝固技术的研究结果,建立了电磁场、温度场与电磁冷坩埚系统主要参数之间的规律性关系。通过改变冷坩埚的横截面形状,初步制备出具有定向凝固组织的TiAl基合金圆、方和扁锭,研究结果表明该方法不但适合于Ti-Al二元合金,而且施与多元多相TiAl基合金也是可行的。通过对成分和组织的控制,所研究的TiAl基合金定向凝固试样的室温拉伸塑性最高达到1.5%左右。最后指出将该方法应用于耐高温的轻质高Nb含量的γ-TiAlNb合金的定向凝固是未来的发展趋势。 相似文献
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高Nb-TiAl基合金锻压饼材的拉伸性能 总被引:1,自引:0,他引:1
用自制的拉伸夹具测度子两种高Nb-TiAl基合金的室温和高温拉伸性能,并对实验结果进行了分析讨论,结果表明,双态组织片层组织有更高的强度,这符合一般TiAl合金的强度规律,且两种合金的室,高温强度均比普通TiAl合金的强度高。 相似文献
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目的 研究凝固模式对TiAl-Nb合金定向凝固组织和力学性能的影响。方法 利用Bridgman定向凝固方法制备了单一β、亚包晶、过包晶以及单一α相4种凝固模式的TiAl-Nb合金,对显微组织进行观察,并进行室、高温拉伸性能测试及断口形貌分析。结果 单一β凝固模式柱状晶明显倾斜,其他凝固模式合金的柱状晶挺直且宽度较均匀,除单一α凝固合金中片层方向近似与定向凝固方向平行外,其他模式凝固合金中大部分片层方向与定向凝固方向呈近45°夹角;拉伸性能结果显示,亚包晶合金室温和高温抗拉强度最高,分别为429和483 MPa,单一α相合金室温和高温抗拉强度最小,分别为281和204 MPa。结论 亚包晶合金其室温和高温拉伸性能均高于其他凝固模式的合金性能,但定向凝固试样制备过程中产生Y2O3颗粒夹杂,导致拉伸试验过程容易形成应力集中,致使定向凝固TiAl-Nb合金较早发生断裂。 相似文献
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Zhongjie PU Jiandong SHI Dunxu ZOU Zengyong ZHONG Central Iron Steel Research Institute Beijing China 《材料科学技术学报》1993,9(6):449-457
Two phases gamma titanium aluminide alloy,Ti-46.5Al-2.5V-1Cr.was investigated to characterizemicrostructures and to define the microstructure/mechanical property relationship.Many kinds ofmicrostructure of gamma and α_2 phases were obtained by heat treatments in the α+γ,α_2+γ and αfields.The effects of microstructure on tensile properties,fracture toughness and J-R resistancecurve at room temperature,were systematically studied.The experimental results showed that themicrostructure had a strong effect on mechanical properties,The duplex microstructure produced byheat treatment at 1250℃×4 h with controlled cooling resulted in the highest ductility of 4.8% tensileelongation,low fracture toughness and crack growth resistance.The fully lamellar microstructureproduced by heat treatment in the α field having large grain sizes resulted in the highest fracturetoughness but the lowest ductility. 相似文献
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Young- Won Kim 《材料科学技术学报》1994,10(2):79-91
The effects of microstructure on the deformation and fracture behaviour of two-phase TiAl alloys were investjgated under monotonic and cyclical loading conditions, over a range of temperatu res.The tensile behaviour is analyzed for deformation temperatures between RT and 950℃, Fracture resistance behaviour and toughening mechanisms at RT and 800℃ are analyzed. and the inverse relationship botween ductility and toughness is explained using the crack initiation toughness. The preliminary results of load-controlled fatigue behaviour at 800℃ are interpreted using the tensile behaviour because deformation structure and fracture modes are similar under these two loading conditions 相似文献
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Long-term thermal stability is often needed for high temperature alloys used in a variety of industrial applications for extended operating lifetimes. In this paper, the effects of thermal exposures or aging on the mechanical properties and microstructure of a Ni–Co–Cr–Si alloy (HAYNES® HR-160® alloy) were studied. It includes both short- and long-term elevated temperature exposures ranging from 649 °C to 1093 °C (1200–2000 F) for duration of 6 min (0.1 h) to 6 years (50,000 h). The residual room temperature (RT) tensile and Charpy-V impact toughness properties were evaluated and correlated to microstructural changes as well as to fracture surfaces of the tensile tested samples. It was found that the RT ductility and impact toughness of the HR-160 alloy decreased continuously with time. A significant percentage of reduction in the ductility occurred in the initial 1000 h of exposure and the subsequent exposure led only to a minimal loss of ductility and impact toughness values. The concomitant microstructural changes were studied using optical metallography, SEM/EDS and X-ray diffraction of extracted residues. The results presented in this paper demonstrated that the HR-160 alloy exhibits good thermal stability characterized by >16% RT elongation after 50,000 h exposures at 649 °C, 760 °C, and 871 °C. 相似文献
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Crack growth in lamellar titanium aluminide 总被引:6,自引:0,他引:6
J.J.M. Arata K.S. Kumar W.A. Curtin A. Needleman 《International Journal of Fracture》2001,111(2):163-189
In-situ compact tension tests on binary lamellar titanium aluminide (TiAl) possessing the colony ``polycrystalline' microstructure illustrate a range of damage phenomena and toughening mechanisms including crack nucleation across colony boundaries, plastic deformation of bridging ligaments, and multiple cracking within colonies. Here, the effects of relative lamellae misorientation and offsets between neighboring colonies on crack growth are investigated computationally through an idealized microstructure of multiple colonies. Within each colony, the brittle Ti3Al lamellae are represented as parallel planes of comparatively low toughness embedded in a matrix of ductile TiAl lamellae that are collectively modeled as an elastic-viscoplastic solid with higher fracture toughness. Plane strain calculations of crack growth are carried out on a compact tension geometry. The calculations are in good qualitative agreement with the in-situ observations, capturing many features of crack growth such as multiple microcrack nucleation and plastic deformation of residual ligaments. Experiments and numerical analyses show that changes in lamellar orientation and alignment across a colony boundary can contribute significantly to the fracture resistance. The numerical results demonstrate that the fracture resistance of these alloys is determined by an intricate interplay between matrix ductility, Ti3Al and TiAl fracture toughnesses, and colony boundary toughness. This suggests the possibility of computationally-guided material optimization through microstructural control of these material properties. 相似文献
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S. TARAFDER S. SIVAPRASAD V. R. RANGANATH 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(9):863-876
A comparative evaluation of fatigue and fracture behaviour of commercially produced cast and forged rail wheels has been made using specimens extracted from various locations of the wheel quadrant. A systematic investigation in the web and rim regions of the wheel quadrant with various notch orientations showed that the forged material exhibited a better intrinsic resistance to fatigue crack growth than the cast material. Since linear elastic fracture mechanics (LEFM) based fracture toughness could not be validated for both the cast and forged wheel material, elastic plastic fracture mechanics (EPFM) based characteristic fracture toughness was used. Results showed that fracture resistance of the forged material is superior to that of the cast material. Cast wheel specimens exhibited unstable crack extension in comparison to substantial stable tearing in forged specimens. Microstructural and fractographic analyses showed that the cast wheel material contained large amounts of inclusions. The poor fracture resistance of cast wheel material is therefore attributed to the inferior material quality. 相似文献
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Comparative study of fatigue and fracture in friction stir and electron beam welds of 24 mm thick titanium alloy Ti‐6Al‐4 V
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Paul D. Edwards M. Ramulu 《Fatigue & Fracture of Engineering Materials & Structures》2016,39(10):1226-1240
In this study, friction stir welding of Ti‐6Al‐4 V was demonstrated in 24 mm thickness material. The microstructure and mechanical properties, fatigue, fracture toughness and crack growth of these thick section friction stir welds were evaluated and compared with electron beam welds produced in the same thickness material. It was found that the friction stir welds possessed a relatively coarse lamellar alpha transformed beta microstructure because of slow cooling from above the transus temperature of the material. The electron beam welds had a fine acicular alpha structure as a result of rapid solidification. The friction stir welds possessed better ductility, fatigue life, fracture toughness and crack growth resistance than the base meal or electron beam welds. Thus, even though friction stir welding is a relatively new process, the performance benefits it offers for the fabrication of heavy gage primary structure make it a more attractive option than the more well‐established electron beam welding method. 相似文献
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Tiantian Huang Wenjie Deng Yujie Zhou Yanyan Cao Chunhua Wei 《Materials Science & Technology》2020,36(15):1648-1654
Strength, ductility and fracture toughness are the most important mechanical properties of engineering materials. In this work, an Al–Zn–Mg–Cu alloy was subjected to multi-directional forging (MF) and ageing treatment. Microstructural evolution was studied by optical and electron microscopy and strength, ductility and fracture toughness were researched. After MF, the dislocation density was increased and the microstructure was refined. The strength and fracture toughness were increased, while the ductility was decreased sharply. Without compromising the strength, the ductility was improved significantly after ageing. The fracture toughness was increased further. The coarse and discontinuously distributed grain boundary precipitates were found to be responsible for higher fracture toughness of the fine-grained structure Al–Zn–Mg–Cu alloy. 相似文献
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《Materials Science & Technology》2013,29(7):840-850
AbstractInvestment castings have been produced in γ-TiAl of composition Ti–48Al–2Nb–2Mn (at.-%) using induction skull melting. The microstructures of the bars were studied in the as cast condition and after hipping and heat treatment. Heat treatment at 1200°C led to a near γ structure whereas treatment at 1350°C resulted in a nearly lamellar structure. However, a duplex structure was retained after treatment at 1300°C. Tensile, fracture toughness, and fatigue crack growth resistance tests have been carried out on specimens machined from different sized bars. The tensile properties increased with decreasing bar diameter but, conversely, both the fracture toughness and fatigue crack growth resistance improved as the bar diameter increased. It has been found that the fracture toughness and fatigue crack growth resistance in nearly lamellar structures were better than those in near γ structures, whereas duplex structures had intermediate properties. However, the tensile properties of duplex structures were better than both near γ and nearly α2 /γ lamellar structures, with optimum values at 35 ± 5% α2 /γ lamellae of ~400 MPa 0·2% proof strength, 470 MPa tensile strength, and 0·9% elongation. 相似文献