Effects of Y content on microstructures and mechanical properties of as-cast Mg-Zn-Nd alloys

The effects of Y addition amount on the microstructures and mechanical properties of as-cast MgZn-Nd alloy have been investigated by using an optical microscope, a scanning electron microscope, backscattered electronic imaging technique, an X-ray diffractometer, a differential thermal analyzer and a universal testing machine. There are three kinds of ternary phases in the Mg-Zn-Y system alloys, such as I phase(Mg3Zn6Y), W phase(Mg3Zn3Y2) and Z or X phase(Mg12Zn Y). The experimental results in the present study indicate that the Mg-Zn-RE(RE includes Y and Nd) ternary phases change from the I + W phases in turn to unique W, W + Z and unique Z as the Y content increases from 0% to 3%. Simultaneously, their distribution gradually changes from small particle-like form to continuous network form. The grain size first decreases as the Y content increases from 0% to 1% Y, then increases when the Y content exceeds 1% and finally decreases again when the content exceeds 3% due to the variation of growth restriction factor caused by the increased Y element and the change of the ternary phases. The hardness continuously increases because of the increased ternary phase amount. The ultimate tensile strength and elongation first increase within the range of 0-1% Y, also due to the increased ternary phase amount and grain refinement, and then decreases because of the grain coarsening, porosity formation and continuous network distribution of the ternary phases. The grain bonding strength of the W phase-containing alloys is quite strong and the W phase is an ideal strengthening phase if a given amount of it distributes in discontinuous and small-sized form. The alloy with 1% Y only has one ternary phase of W, but has the best combination of mechanical properties. The fracture regimes of these alloys always present a transgranular mode.     

Zn添加对挤压态Mg-Zn-Ce-Zr合金微观组织及力学性能的影响

通过光学显微镜(OM)、扫描电镜(SEM)、背散射电子衍射(EBSD)和力学性能检测,研究不同Zn含量(0.5%、1.5%和2.0%(质量分数))的Mg-Zn-Ce-Zr合金在温度为350℃,挤压比为9,挤压速率为10 mm/s条件下挤压后的微观组织和力学性能。结果表明:随着Zn含量的增加,铸态下晶间析出相明显增多;挤压后,Zn含量对合金晶粒度的影响不大,但棒材的丝织构随Zn含量增加而增强。由于第二相粒子的强化作用,随Zn含量增加,合金的拉伸屈服强度从158 MPa增加到192 MPa,而抗拉强度从219 MPa提高到246 MPa。由于丝织构强度增加,合金塑性随Zn含量增加从33%降低至18%,添加0.5%Zn合金的伸长率和拉压对称性最好。     

钙与电磁搅拌对Mg-Li-Al合金微观组织和力学性能的影响

以Mg-8%Li-3%Al合金为基体,研究合金化元素Ca以及Ca与电磁搅拌复合作用对其凝固组织和力学性能的影响,并探讨其化学成分、组织结构和力学性能间的关系。结果表明:合金化元素Ca以及Ca与电磁搅拌复合作用都能改善Mg-8%Li-3%Al合金的凝固组织和力学性能;当铸态合金中Ca含量为0.5%(质量分数)时,合金中β相细小均匀,室温抗拉强度和伸长率分别达到188.93MPa和11.35%;施加80V电磁场电压以及加入0.5%Ca后,晶粒组织均匀有序,布氏硬度、抗拉强度和伸长率分别为67.5HB、203.8MPa和7.7%。     

B2O3对铸态Mg-Al-Ti-B合金的显微组织与力学性能的影响

采用机械合金化制备的 Mg?Al?Ti?B 合金,其微观组织的均匀性较差,而且致密性也不好。为了提高Mg?Al?Ti?B合金微观组织的均匀性和致密性,使其力学性能得到改善,制备了铸态Mg?9Al?6Ti合金。采用金相显微镜、扫描电镜、X射线衍射与力学性能测试等手段,研究B2O3对Mg?9Al?6Ti (质量分数,%)合金的显微组织与力学性能的影响。结果表明：添加3%的B2O3使Mg?Al?Ti?B合金的晶粒尺寸减小到12μm,Ti颗粒完全消失,沉淀相Mg17Al12减少,而TiAl3相增多。由于新沉淀相MgB6和Ti3B4的析出,Mg?9Al?6Ti?3B2O3合金的结构变得均匀,平均硬度为HV77.1,平均抗拉强度、屈服强度和伸长率分别是171.2 MPa、113.5 MPa和5.2%。     

TiAl基合金的工艺—显微组织—力学性能关系

因密度、比刚度、高温比强度和阻燃性等方面的优势,TiAl基金属间化合物被认为是最有应用潜力的新一代结构材料。室温脆性以及延性、蠕变性能和其它性能的平衡是阻碍TiAl基合金作为高温结构材料实际应用的主要障碍。在分析合金化对组织与性能的影响及机理、加工／热处理 对组织与性能的影响、变形和断裂机制、显微组织与拉伸性能的关系、抗氧化性及改善、蠕变性能与蠕变机制的基础上,论述了TiAl基合金的工艺－显微组织－力学性能关系。     

Effects of Cu， Ni， Mn and Mo on the austemperability， microstructures and mechanical properties of ADI weld metal

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Effects of aging on the microstructures and mechanical properties of extruded AM50 ＋ xCa magnesium alloys

The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50 ＋ xCa al- loys increased initially to its peak, and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature, the hardness of the AM50 ＋ 2Ca ahoy decreased, whereas the hardness of AM50 and AM50 ＋ 1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50 ＋ 1Ca alloys increased after aging treatment for the precipitation of Mg17Al12 phase, which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature, their tensile strengths increased. For AM50 ＋ 2Ca alloy, the tensile strength declined after aging at 150℃ and 175℃, while it increased slightly at 200℃. The ductility of AM50 ＋ xCa alloys （x = 0, 1, 2 wt.%） declined after aging treatment.     

钆对Mg-8Li-4Zn-xGd合金铸态组织与力学性能的影响

采用锂盐熔剂保护熔铸Mg-8Li-4Zn-xGd(x=1,3,5)合金铸锭,研究钆含量对铸态合金组织和力学性能的影响。结果表明:Mg-8Li-4Zn-xGd合金基体由α-Mg(HCP)和β-Li(BCC)双相构成。随着钆含量的增加,Mg₅Gd共晶相和Zn₁₂Gd化合物相逐渐连成网状,将基体α+β双相隔离成20～40μm的等轴状或类似于铸铁中的共晶团状,可有效细化α-Mg相和连续的β-Li相;组织中大颗粒Mg₂Zn₁₁相弥散分布在β-Li相内,Mg₅₁Zn₂₀相分布在α-Mg晶界处;锌元素还可以在β-Li相中析出细小弥散分布的MgZn相,其数量随钆含量的增加而增加,可直接弥散强化β-Li相。此外,锌和钆对合金硬度的影响较大,随着钆含量的增加,合金的抗拉强度提高,但伸长率降低。     

Gd含量对Al-Zn-Mg-Cu-Zr合金微观组织与力学性能的影响

采用铸锭冶金工艺制备6种Gd含量不同的A1-Zn-Mg-Cu-Zr-xGd合金。采用金相观察、力学性能测试、扫描电镜、电子探针及透射电镜等分析手段,研究质量分数x,分别为0%、0.10%、0.15%、0.20%、0.25%和0.30%的Gd对基体合金铸态及时效态显微组织和力学性能的影响。结果表明:Gd含量对A1-Zn-Mg-Cu-Zr合金的微观组织和力学性能的影响显著,当Gd含量低于0.25%时,随Gd含量的增加细化效果、强度以及伸长率都增加;当Gd含量为0.25%时,铸态组织中基体晶粒最小,达到32μm左右;此时T6态合金组织的强度和伸长率达到最高,抗拉强为624.54 MPa,屈服强度为595.00 MPa,伸长率为13.3%,且固溶组织具有良好的抗再结晶作用;而当Gd含量超过0.25%时,合金的微观的组织与力学性能变差。     

Sc对Al-Zn-Mg-Cu-Zr合金铸态组织和力学性能的影响

采用金相显微镜、扫描电镜和能谱分析,研究Sc对Al-9.0Zn-2.5Mg-2.5Cu-0.15Zr合金铸态组织和力学性能的影响。结果表明,添加0.20%-0.60%的Sc,会使合金的铸态组织由粗大的树枝晶变为等轴晶,并使Cu的偏聚减轻,且Sc含量越高,合金铸态组织越细,Sc含量为0.60%的合金铸态组织最细小;随着Sc含量的增加,合金的抗拉强度升高,T6态时,Sc含量为0.60%的合金抗拉强度高达783.9 MPa。从熔体中析出的Al3（Sc,Zr）一次粒子具有与α（Al）基体相同的FCC晶格,晶格常数接近,可有效地细化合金的铸态组织。合金强化机理主要为Al3（Sc,Zr）引起的细晶强化、亚结构强化和沉淀强化。     

Effects of Nb and Al on the microstructures and mechanical properties of high Nb containing TiAl base alloys

The influence of Nb and Al contents on the microstructure and yield strength of high Nb containing TiAl base alloys was investigated. The experimental results show that the yield strength at 900 °C of the alloys with the same type of microstructure, such as fully lamellar (FL), nearly lamellar (NL) and degraded fully lamellar (DFL), increases with increasing Nb content and decreasing Al content in the composition range of 0–10 at.% Nb and 44–49 at.% Al. DFL is the degraded form of FL microstructure after exposure at 1050 °C for 30 h. It is shown that the Nb addition in the alloys increases the value of the σ₀ term in the Hall–Petch relation of yield stress vs. lamellar spacing. This result has been related to TEM observations of dislocation structure in deformed specimens. The observations indicated that high level of Nb solute in the γ-TiAl matrix leads to a high critical resolved shear stress (CRSS) of dislocation loops. High Nb addition also reduces the degradation rate of FL microstructure after exposure at 1050 °C for 30 h. Both effects of high Nb addition are related to the change of the directionality of Ti–Ti (Nb) and Nb–Al bonds in the lattice. The decrease in Al content results in an increase in the volume fraction of α₂ phase, which leads to a decrease in the lamellar spacing of the lamellar structure. The high temperature strength of the alloys is determined by the lamellar spacing λ through the Hall–Petch equation k_λλ^−1/2.     

纳米多晶Ni微观结构与力学性能的分子动力学模拟

运用分子动力学技术,结合分析型嵌入原子方法(AEAM)模拟计算了平均晶粒尺寸为2.09～5.23 nm的纳米多晶Ni的微观结构和力学性能.从原子能量分布、径向分布函数(RDF)、局域晶序结构的角度分析了纳米多晶Ni的晶界和晶粒结构,发现晶界部分所占的比例随晶粒尺寸的减小明显提高,结构与普通微晶的相似,纳米晶体的结合能较普通晶体的低.单向拉伸模拟结果表明:纳米多晶Ni的强度与晶粒尺寸之间出现反常Hall-Petch关系;弹性模量的降低与纳米尺度结构特征相关.     

Sr对AZ91镁合金组织及力学性能的影响

采用光学显微镜、扫描电子显微镜和X射线衍射仪等研究Sr对AZ91镁合金组织及力学性能的影响.结果表明:添加微量Sr可以细化并离散AZ91合金的铸态共晶组织,在合金晶界处Sr与Al生成多角块状或杆状的Al4Sr高熔点相;当Sr含量为0.2%时,AZ91-0.2Sr合金的综合力学性能最优,AZ91-Sr合金的时效进程与AZ91合金相比明显被抑制.由于这些析出相及合金晶界附近Al4Sr高熔点相的强化作用,AZ91-0.2Sr合金经T6处理后的室温和高温力学性能皆优于原AZ91合金的.     

Ti和Al的交互作用对Nb-Ti-Si-Al合金微观组织和力学性能的影响

Nb-Si基超高温合金由于具有低密度和高熔点,有望取代当前先进的Ni基高温合金,成为新型的高温结构材料。Ti和Al均为对Nb-Si基合金有益的合金化元素。在文献中,通常对低含量(≤ 3 at. % )Al进行合金化研究,在此情形下不会出现Nb-Al金属间化合物相。Nb-Al金属间化合物中Nb₃Al和Nb₂Al具有良好的强度和抗蠕变性能,NbAl₃则是重要的高温结构材料,而目前公开文献中关于Nb-Si基合金中含有Nb-Al金属间化合物的报道较少。因此,本文重点关注高Al含量对合金中Nb-Al金属间化合物形成的影响,研究两个高Al含量的Nb-Ti-Si-Al合金(A2: Nb-18Ti-14Si-9Al、A4: Nb-21Ti-14Si-9Al)的微观组织和力学性能,其中设计A4合金是为了分析Ti含量变化的影响。A2合金由(Nb)、Nb₅Si₃和Nb₃Al三相组成,而A4合金由(Nb)和Nb₅Si₃两相组成。A2和A4合金的室温断裂韧性分别为11.1 MPa.m_1/2和10.9 MPa.m_1/2,同时对两个合金进行微压痕测试,以表征合金在微观尺度的力学性能。     

Effects of Ni addition on mechanical properties and corrosion behaviors of coarse-grained WC-10(Co,Ni) cemented carbides

The effects of the Ni content on the mechanical properties and corrosion behavior of coarse-grained WC-10Co cemented carbide, with a grain size of 3.5 μm, were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electrochemical measurements, and mechanical property tests. The results indicate that the strength and toughness are improved with the addition of 2 wt% Ni without sacrificing hardness. Furthermore, the existence of Ni can decrease the corrosion current density (i_corr) of WC-10Co cemented carbide in both 0.1 M HCl and 0.1 M NaOH solutions. The SEM and XPS results reveal that only a minor amount of WO₃ formed in the corroded surface in HCl solution. The corrosion behavior was determined by the dissolution of the binder phase, and Ni can develop the charge-change resistance (R_ct). Contrarily, the Co binder phase were oxidized to a dense passive film (Co(OH)₂ and Co₃O₄) in NaOH solution, and the addition of Ni was conducive to the enhancement of the diffusion resistance (R_f). This may give insights into adding an appropriate Ni content in coarse-grained WC-Co cemented carbide, in which the wear and corrosion of the components coexist.     

Effects of Ag,Co, and Ge additions on microstructure and mechanical properties of Be-Al alloy fabricated by investment casting

The effects of Ag, Co, and Ge additions on microstructure and mechanical properties of Be-35Al (wt.%) alloys fabricated by investment casting were studied. The results reveal that the trace metals 1.5wt.% Ag, 0.7wt.% Co, and 0.8wt.% Ge additions do not change the nucleation temperature of Be phase. However, the nucleation temperature of the Al phase decreases from 642 °C to 630 °C by DSC due to the Ge addition. The strength of the alloys sharply increases due to the dissolution of the Ag and Ge solutes into the Al phase and the Co into the Be phase characterized by SEM and EDS. Obviously, the strength of Be-Al-Ag-Co-Ge alloy is improved by the solution strengthening. Furthermore, a few Ag₃Al particles contribute to the strength of the Al phase. Be-Fe-Al ternary intermetallic compounds which can effectively reduce the negative effect of an impurity element Fe on the mechanical properties of Be-Al alloys are also found by XRD and EDS.

     

Effect of Sc and Zr on microstructures and mechanical properties of as-cast Al-Mg-Si-Mn alloys

Microstructures of as-cast Al-Mg-Si-Mn alloys with and without Sc and Zr were investigated by optical microscopy, scanning electronic microscopy(SEM) and energy dispersion spectrum analysis. Addition of 0.2%-0.4% Sc can refine the grain size and change the growth morphology from dendritic to fine equi-axial crystal. The higher the addition of Sc, the finer the as-cast grain size. The tensile strength is increased by more than 30% with 0.4% Sc. Moreover, an addition of 0.1%-0.2% Zr is able to refine grain size and change the growth morphology from dendritic to equi-axial grain too, but less effective. However, Zr is found to increase the ductility of the cast alloys, and the elongation is increased to 11.97% with 0.2% Zr.     

合金化对TiAl合金高温变形行为的影响

TiAl合金的热加工（锻造、热挤压、板材轧制等）窗口窄,高温变形能力差,室温脆性大等成为限制其应用的关键因素,本文主要综述了合金成分对TiAl合金热变形加工以及超塑性成形影响等方面的研究现状,从TiAl合金的晶体结构、β相含量、显微组织细化、热变形激活能四个方面探讨了合金成分对TiAl合金热变形加工的影响,并指出合金化方式提高TiAl合金热变形加工能力应该遵循的几点原则,以及TiAl合金热变形加工的未来发展趋势。     

合金化和形变处理对Cu-Mg-Te-Y合金组织性能的影响

制备具有高强高导性能的铜合金,研究添加Mg和微量的Y对合金的组织和性能的影响。通过变形和退火等工艺处理后,Cu-0.47Mg-0.2Te-0.04Y合金的性能指标可达到：抗拉强度510 MPa,伸长率11%,导电率大于63% IACS。稀土元素Y的熔体净化作用、细晶强化作用和添加适量Mg产生的固溶强化作用能够提高合金的力学性能和导电率。