Fatigue crack growth rates and fracture toughness of rapidly solidified Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloys

The room-temperature fatigue crack growth rates (FCGR) and fracture toughness were evaluated for different crack plane orientations of an Al-8.5 Pct Fe-1.2 Pct V-1.7 Pct Si alloy produced by planar flow casting (PFC) and atomized melt deposition (AMD) processes. For the alloy produced by the PFC process, properties were determined in six different orientations, including the short transverse directions S-T and S-L. Diffusion bonding and adhesive bonding methods were used to prepare specimens for determining FCGR and fracture toughness in the short transverse direction. Interparticle boundaries control fracture properties in the alloy produced by PFC. Fracture toughness of the PFC alloy varies from 13.4 MPa√m to 30.8 MPa√m, depending on the orientation of the crack plane relative to the interparticle boundaries. Fatigue crack growth resistance and fracture toughness are greater in the L-T, L-S, and T-S directions than in the T-L, S-T, and S-L orientations. The alloy produced by AMD does not exhibit anisotropy in fracture toughness and fatigue crack growth resistance in the as-deposited condition or in the extruded condition. The fracture toughness varies from 17.2 MPa√m to 18.5 MPa√m for the as-deposited condition and from 19.8 MPa√m to 21.0 MPa√m for the extruded condition. Fracture properties are controlled by intrinsic factors in the alloy produced by AMD. Fatigue crack growth rates of the AMD alloy are comparable to those of the PFC alloy in the L-T orientation. The crack propagation modes were studied by optical metallographic examination of crack-microstructure interactions and scanning electron microscopy of the fracture surfaces.     

High-temperature creep in an Al-8.5Fe-1.3V-1.7Si alloy processed by rapid solidification

The creep behavior of an Al-8.5Fe-1.3V-1.7Si alloy processed by rapid solidification is investigated at three temperatures ranging from 623 to 723 K. The measured minimum creep strain rates cover seven orders of magnitude. The creep behavior is associated with the true threshold stress, decreasing with increasing temperature more strongly than the shear modulus of aluminum. The minimum creep strain rate is controlled by the lattice diffusion in the alloy matrix, and the true stress exponent is close to 5. The apparent activation energy of creep depends strongly on both applied stress and temperature and is generally much higher than the activation enthalpy of lattice self-diffusion in aluminum. Also, the apparent stress exponent of minimum creep strain rate depends on applied stress as well as on temperature and is generally much higher than the true stress exponent. This behavior of both the apparent activation energy and apparent stress exponent is accounted for by the strong temperature dependence of the threshold stress-to-shear modulus ratio. The true threshold creep behavior of the alloy is interpreted in terms of athermal detachment of dislocations from fine incoherent Al₁₂(Fe, V)₃Si phase particles, admitting a temperature dependence of the relaxation factor characterizing the strength of the attractive dislocation/particle interaction.     

锻造对喷射成形Al-8.5Fe-1.3V-1.7Si合金组织和性能的影响

采用喷射成形和锻造工艺制备了Al-8.5Fe-1.3V-1.7Si合金．通过金相、扫描电镜和力学性能测试等实验，对锻件组织和性能进行了分析。结果表明：“闷车＋包套锻造”工艺对喷射成形Al-8.5Fe-1.3V-1.7Si合金坯件的致密化效果好于用自由锻造和包套锻造致密化的合金，采用该工艺可以制备出组织和性能优良的耐热铝合金材料。“闷车＋包套锻造”锻件在室温下的抗拉强度（σb）达到407MPa，屈服强度（σ0.2）达到344MPa，延伸率（δ5）为7．6％；在315℃，锻件的σb，σ0.2，σ5分别为222，216MPa，7．2％。     

喷射成形Al-8.5Fe-1.1V-1.9Si耐热铝合金的组织演变及性能分析

研究了喷射成形Al—8．5Fe—1．1V—1．9Si耐热铝合金组织结构的演变规律，测试了挤压态合金在室温及高温条件下的力学性能。与铸态组织特征相比较，喷射成形工艺有效地消除了铸态合金中粗大的富Fe析出相，获得了细小均匀的组织结构。利用OM，SEM，TEM，XRD等材料分析测试手段，探索了材料中可能的组织演变过程及规律，结果表明：喷射成形制备的Al—Fe—V—Si耐热铝合金中，形成了大量的弥散分布的球状相，有效的保证了合金在室温及高温下的力学性能。室温下，合金的抗拉强度可以达到445MPa，屈服强度也达到了398MPa，延伸率为16％；在315℃，合金的抗拉强度和屈服强度分别为229和209MPa。     

喷射成形Al-8.5Fe-1.1V-1.9Si耐热铝合金中弥散强化相体积分数的确定

利用喷射成形工艺制备了Al 8.5Fe 1.1V 1.9Si耐热铝合金 ,观察了合金中耐热相的形貌 ,发现弥散强化相的尺寸在 5 0～ 10 0nm之间。采用Rietveld全谱拟合的方法初步测定了铝合金中弥散强化相的重量百分数为 2 8.4% ,通过换算得出弥散强化相的体积分数为 2 2 .4%。同时分析了与平面流铸造 (PFC)所制备的合金中耐热相体积分数的差异 ,并探讨了合金耐热相体积分数的变化对合金力学性能的影响     

Fabrication and properties of heavy section extrusions of Ti-6Al-6V-2Sn and Ti-8Mo-8V-2Fe-3AI alloys

This study is concerned with the fabrication in heavy section of the titanium alloys Ti-8Mo-8V-2Fe-3Al (Ti-8823) and Ti-6Al-6V-2Sn (Ti-662). The technique utilized to achieve 84 pct reduction during the extrusion of heavy section cylindrical hollows is given. The response to subsequent aging of both alloys is described in terms of the effect on important mechanical properties such as yield and ultimate tensile strength, ductility and fracture toughness. For the Ti-8823 alloy extruded in heavy section, it is shown that the optimum heat treatment consists of aging directly after hot working rather than the more common solution treatment and age cycle. With the former heat treatment, uniform through the thickness mechanical properties are obtained. Uniform mechanical properties are also obtained through the section of the Ti-662 extrusion with a solutionizing and overaging heat treatment.     

Microstructure and mechanical properties of Mg-14Li-1Al-0.3La alloys produced by two-pass extrusion

The microstructure of as-cast and extruded Mg-14 Li-1 Al-(0, 0.3) La alloys was examined with XRD,OM, SEM, and EDS. The mechanical properties of the extruded specimens with and without La were compared. The results show that La addition has an obvious effect on the microstructure of the as-cast LA141 alloy by reducing the average grain size from 600 to 220 μm. β-Li and LiMgAl_2 phases are observed in both alloys, and long-rod-shaped Al_2 La phase is also observed in the La containing alloy. After extrusion, Al_2 La phases are short-rod-shaped and distribute evenly in the alloy. LAl41-0.3 La alloy has higher elongation(34%), which is attributed to refined microstructure and weak texture due to shortrod-like Al_2 La phase.     

放电等离子烧结TiAl基合金的显微组织及力学性能

以Ti-47.5Al-2.5V-1.0Cr合金粉末为原料,采用放电等离子烧结工艺制备出TiAl基合金,并研究了制备工艺、显微组织与室温力学性能三者的关系.结果表明,采用放电等离子烧结方法可制备出致密度高、组织均匀的TiAl基合金.烧结温度对合金的显微组织影响显著,且其室温力学性能与显微组织密切相关,显微组织越细小,室温强度和塑性越高.当烧结温度为1100℃时,制备出的TiAl-V-Cr合金显微组织类型为细小双态组织,具有35.2%的压缩率和3321MPa的断裂强度,显示出较好的室温压缩性能.     

铸态和沉积态Al-25Si-5Fe-3Cu合金的显微组织与相形成

采用常规铸造和喷射成形工艺制备了含硅达25%(质量分数)的过共晶Al-Si合金,利用SEM(EDS)、XRD和DSC等分析方法对合金的显微组织和相熔解析出进行了分析研究.结果表明,铸态合金含有粗大块状初晶Si相和粗大针片状含铁相,而喷射成形工艺能够使二者的尺寸、形貌发生改变而有利于合金性能的提高.同时,铸态和沉积态合金中均含有基体Al、初晶Si和Al₂Cu相,不同的是铸态合金中含铁相主要为δ-Al₄FeSi₂相,而沉积态合金中以β-Al₅FeSi相为主.分析其原因主要是糊状层的存在引起沉积坯冷却速度降低而导致沉积坯中发生δ-Al₄FeSi₂相的转变及共晶组织增加,致使沉积态合金中β-Al₅FeSi相为主要含铁相.采用DSC实验对沉积态合金在熔化和凝固过程中发生的反应进行了讨论.     

The mechanical properties of ceramic composites produced by melt oxidation

The strength and fracture toughness of a range of DMOX materials, with and without SiC particulates, have been measured. The strength has been shown to correlate with the SiC particulate size and to be consistent with a model based on the expansion misfit between the particulates and the matrix. The toughness has contributions for both the residual alloy and the SiC. The former has been shown to conform well with the expectations of models based on plastic dissipation in the alloy. The influence of the SiC is found to be strongly dependent on the particulate size and is qualitatively consistent with a contribution to toughness from frictional dissipation at debonded SiC/Al₂O₃ interfaces.     

A comparison study of microstructure and mechanical properties of Ti-24Al-14Nb-3V-0.5Mo with and without Si

A comparative study has been made of the room- and elevated-temperature properties, room-temperature fracture toughness, fatigue-crack propagation rates, and 650 °C creep properties of Ti-24Al-14Nb-3V-0.5Mo with and without 0.9 at. pct Si. Both alloys have microstructures consisting of the α ₂, B2, and the orthorhombic O phase, with different proportions of the α ₂ phase relative to the (O + B2) mixtures, depending on solution-treatment temperature. The alloy with a Si addition contains additional primary ζ-Ti₅Si₃ particles distributed in the (O + B2) matrix. Tests of mechanical properties showed that the incorporation of a small fraction (about 0.03 by volume) of the Ti₅Si₃ phase leads to greater room-temperature and elevated-temperature strengths, but lower room-temperature elongations and fracture toughness as compared with the base alloy. Alloys containing greater volume fractions of the α ₂ phase exhibited better tensile ductility, and this was attributed to the concurrent stabilization of the B2 phase. Examination of tensile-tested and fatigued specimens indicates that the primary failure mode of the alloys, regardless of Si addition, was due to the brittleness of the α ₂ phase; the silicide particles that debonded from the matrix also contribute to cracking in the monotonic loading mode. Up to a 20 pct improvement in creep-rupture life was observed in the Si-containing alloys, and this was interpreted in terms of the solute-strengthening effect of Si. While the incorporated Ti₅Si₃ phase has an unfavorable effect on ductility and room-temperature fracture toughness, the difference in fatigue-crack propagation rates between the alloys with and without Si is minimal. It is concluded that the controlling factor for the fatigue failure in orthorhombic alloys is related to the (α ₂ + O + B2) microstructure, instead of the Ti₅Si₃ particles.     

Microstructures and properties of CoCrCuFeNiMox high-entropy alloys fabricated by mechanical alloying and spark plasma sintering

CoCrCuFeNiMox (x values in molar ratio, x?=?0, 0.2, 0.4 and 0.8) high-entropy alloys were prepared by mechanical alloying and spark plasma sintering method. The effects of Mo addition on microstructure and mechanical properties were investigated. The X-ray diffraction (XRD) result showed that the addition of Mo into CoCrCuFeNi high-entropy alloy (HEA) changed the original phase constitution from FCC to FCC?+?σ?+?μ and the peak intensity of (1 1 1) shifted to the left and decreased steadily. The field emission scanning electron microscope confirmed that the Cu-rich second FCC phase disappeared and the σ phase with a tetragonal structure expanded as the Mo content was increased. Additionally, a high density of dimple-like features were seen in CoCrCuFeNi HEA while typical quasi-cleavage facets could be observed from the fracture surfaces of the HEAs with the addition of Mo. The Mo0.8 alloy showed a good wear resistant and appropriate strength with fracture strain 22.70%, fraction coefficient 0.65, hardness 530?HV and compressive strength 1448?MPa.

Special theme block on high entropy alloys, guest edited by Paula Alvaredo Olmos, Universidad Carlos III de Madrid, Spain, and Sheng Guo, Chalmers University, Gothenburg, Sweden.     

Ti-6Al-7Nb合金随温度的组织与性能演变

为揭示Ti-6Al-7Nb合金随热处理温度的不同,显微组织、力学性能及相组成的变化规律,研究了合金在650℃-1030℃热处理空冷条件下的组织演变,进行室温力学性能测试与XRD分析。结果表明：650℃属于时效温度,热加工得到的原β转变组织中析出细小的α相,合金的强度和弹性模量有所提高。700℃-850℃之间进行热处理,可以获得良好的综合性能,满足相关标准要求。合金弹性模量处于94-100 GPa。950℃-1030℃温度范围内,随着温度的升高,由于二次针状α相的析出,或者生成α"相,呈现强度上升,塑性下降的趋势。650℃、850℃两个温度热处理后,Ti-6Al-7Nb合金的XRD图谱未出现β相的衍射峰,均为α相的衍射峰。1030℃热处理后,α"相具有较强的(002)、(101)衍射峰,其它晶面的衍射峰能量很弱。合金弹性模量达最大值108GPa。通过金相观察,推算Ti-6Al-7Nb合金α+β→β转变的开始温度处于900℃-920℃,终了温度处于1010℃-1030℃。     

Microstructures,mechanical properties,and electrical resistivity of rapidly quenched Fe-Cr-Al alloys

By the rapid quenching technique, ductile supersaturated ferrite solid solution with high hardness and strength as well as unusual electrical properties has been found in Fe-Cr-Al ternary system. This formation range is limited to less than about 35 at. pct Cr and 23 at. pct Al. The ferrite phase has fine grains of about 10 μm in diameter. Their hardness, yield strength, and tensile fracture strength increase with increase in the amounts of chromium and aluminum, and the highest values reach about 290 DPN, 720 MPa, and 740 MPa. These alloys are so ductile that no cracks are observed even after closely contacted bending test. The good strength and ductility remain almost unchanged on tempering for one hour until heated to about 923 K where a large amount of Cr₂Al compound begins to precipitate preferentially along the grain boundaries of the ferrite phase. The room-temperature resistivity increases with increasing chromium and aluminum contents and reaches as high as 1.86 μ Ώ m for Fe₅₀Cr₃₀Al₂₀ alloy. Also, the temperature coefficient of resistivity in the temperature range between room temperature and 773 K decreases with increasing chromium and aluminum contents and becomes zero in the vicinity of 20 to 30 at. pct Cr and 15 at. pct Al. Thus, the present alloys may be attractive as fine gauge high-resistance and/or standard-resistance wires and plates because of the unusual electrical properties combined with high strength and good ductility. formerly with the Research Staff of Tohoku University formerly Graduate Student of Tohoku University,     

Structure and mechanical properties of Al-Fe system-base microcrystalline alloys produced by powder metallurgy methods

Translated from Poroshkovaya Metallurgiya, No. 4(340), pp. 93–98, April, 1991.     

粉末冶金法低成本制备Ti-1Al-8V-5Fe合金的组织和性能

本文以低成本Fe V80中间合金粉末为原料,用粉末冶金法制备了Ti185合金,并对其组织和力学性能进行分析检测。实验结果表明,该方法制备出的烧结合金组织均匀,无元素偏析,未产生传统熔炼方法中不可避免的"β斑";其抗拉强度可达到840±20 MPa、屈服强度可达到772±15 MPa、延伸率为5.4±0.3%,综合性能可与市售Ti185合金坯料媲美。     

The structure and mechanical properties of fine diameter Al-1pct Si wire

Metallurgical and Materials Transactions B - The structure and mechanical properties of fine diameter Al-1pct Si alloy wires have been investigated. The mechanical behavior of wires as received...     

Production of heat-resistant EP220 and EP929 alloys by high-temperature treatment of melt

Analysis of samples of EP220 and EP929 alloys in the liquid and solid state permits the determination of the parameters for high-temperature melt treatment in their production. On heating to specific temperatures, the structure of the liquid alloys moves closer to equilibrium. In the solidification of such melt, the cast metal formed is characterized by finer grain structure, greater dispersity of the dendrites, and greater density and microhardness of the matrix. Industrial adoption of high-temperature melt treatment will improve plasticity, increase the long-term strength, and boost the product yield. The proposed technology does not fully utilize the potential of the alloy structure obtained after high-temperature melt treatment. The effect may be amplified by more prolonged holding of the melt at 1650°C and by optimization of the vacuum-arc heating, deformation, and heat treatment, in the light of the structural changes in the experimental samples of solid metal.