Structure and mechanical properties of the annealed TZAV-30 alloy

The Ti–30Zr–5Al–3V (wt.%, TZAV-30) alloy having good mechanical properties is a potential structural material to apply in the aerospace industry. The microstructure and mechanical properties of ZTAV-30 alloy underwent various annealing heat treatments were investigated. The specimens annealed from 500 to 800 °C are composed of α and β two phases. No compound is detected in specimens annealed in that temperature range. The microstructure of annealed specimens is characterized as a typical basketweave microstructure. Three microstructural parameters, thickness of plate α phase, relative fraction of β phase and aspect ratio of α grains, were measured in those annealed specimens. As the alloy annealed in the range from 500 to 800 °C, the average thickness of plate α grains increases with the increasing annealing temperature from 500 to 700 °C but decreases while annealed at 800 °C. The fraction of retained β phase increases with annealing temperature. And the aspect ratio of plate α grains decreases firstly but increases while the annealing temperature is higher than 700 °C. As the variation of those three microstructural parameters, the strength of examined alloy varies from 1269 to 1355 MPa for tensile strength and from 1101 to 1190 MPa for yield strength, inversely, the elongation changes in the range from 12.7% to 8.4%. The strengthening and toughening mechanism of the TZAV-30 alloy with basketweave microstructure is also discussed in this paper.     

Tuning the near room temperature oxidation behavior of high-entropy alloy nanoparticles

Understanding the oxidation behavior of high-entropy alloys(HEAs)is essential to their practical applications.Here we conducted in situ environmental transmissi...     

Effect of Mo-alloyed layer on oxidation behavior of TiAl-based alloy

A Mo-alloyed layer was prepared on a TiAl-based alloy using plasma surface metallurgy technique. The microstructure and oxidation behavior of the alloyed TiAl were investigated. The surface alloyed layer with a thickness of approx. 40 μm and a gradient concentration distribution was composed of Ti₂MoAl, TiAl and Mo phases. Cycling oxidation test was carried out at 850 °C in air under an atmospheric pressure. The result of the oxidation kinetics test shows that the mass gain of the Mo-alloyed TiAl after exposure for 100 h was less than the value of the untreated TiAl substrate, exhibiting an improved oxidation resistance. The Al₂O₃-rich mixed oxide scale formed on the alloyed TiAl is supposed to be the main reason of the beneficial effect on the improvement of oxidation resistance for TiAl-based alloy.     

BT20合金高温变形行为的研究

为实现BT20合金锻造的数值模拟和合理制定其热成形工艺参数,利用Thermecmastor-Z型热模拟试验机对该材料在热成形条件下的变形抗力进行了研究,考察了变形温度、应变速率及变形程度与变形抗力之间的关系,并利用冶金学方法对其进行了分析.结果表明,应变速率和变形温度的变化强烈影响着合金流变应力的大小,流变应力随变形温度升高而降低,随应变速率提高而增大.通过真实σ-ε曲线,回归出可综合反映锻造热力参数对材料成形性能影响的本构方程.     

Correlation of alloy microstructure with oxidation behavior in chromia-forming intermetallic-reinforced Cr alloys

Abstract

The oxidation behavior of the Cr(X) solid solution and intermetallic Cr₂X Laves phases (X = Nb, Ta) was studied individually and in combination at 1,100°C in humid air. The two-phase Cr(Ta) + Cr₂Ta alloys exhibited superior oxidation resistance to either the single-phase Cr(Ta) or the single-phase Cr₂Ta alloys. However, the two-phase Cr(Nb) + Cr₂Nb alloys exhibited lower oxidation resistance than either the single-phase Cr(Nb) or Cr₂Nb alloys. The two-phase Cr(Ta) + Cr₂Ta alloys were also found to exhibit superior oxidation resistance to the two-phase Cr(Nb) + Cr₂Nb alloys. This was hypothesized to be related to the lower amount of the Cr₂X phase in the Cr(Ta)–Cr₂Ta eutectic and to the lower solubility of Ta in the Cr(X) phase, relative to the Cr–Nb system. Both of these factors resulted in significantly less oxidation and nitridation in the Cr(Ta) + Cr₂Ta alloys.     

Effect of yttrium on high temperature oxidation behavior of Ni-Al-Mo-B alloy IC6

A variety of experimental techniques have been used to study the effect of yttrium on the high temperature cyclic oxidation behavior of a directionally solidified (DS) Ni-Al-Mo-B alloy IC6. The cyclic oxidation resistance of alloy IC6 is substantially improved by adding proper amount of yttrium, which is resulted from several beneficial roles played by yttrium. Yttrium decreases the harmful effect of sulfur to the adherence between the oxides scale and the substrate, and the depth of the diffusion layer by inhibiting cationic transportation. Yttrium promotes the selective oxidation of aluminum and decreases the proportion of NiO region in the surface oxide scale. Yttrium migrates to the oxide grain boundaries and promotes the formation of a fine close packed oxide grain structure, and hence improves the mechanical strength of the grain boundaries.     

Oxidation behavior and effect of oxidation on tensile properties of Ti60 alloy

Oxidation behavior of a near-alpha Ti60 titanium alloy was investigated in the temperature range of 600–750 °C for up to 100 h exposure. The results showed that the oxidation kinetics of Ti60 alloy followed parabolic kinetics below 700 °C but parabolic-linear kinetics above 700 °C. The total activation energy was calculated to be 256 kJ/mol over the whole temperature range. The oxidation products were TiO₂ after thermal exposure at 700 °C for 100 h, but a mixture of TiO₂ and a small amount of Al₂O₃ for the specimens oxidized at 750 °C for 50 h. The grain boundaries were preferred sites for oxidation products formation during the oxidation. The tensile tests were performed at room temperature for specimens before and after oxidation. Both of the strength and ductility decreased for the specimens with oxide scale. However, both of them increased when the oxide scale was removed before testing.     

2618铝合金后摇臂等温体积成形工艺的研究

根据后摇臂技术条件要求,确定了等温成形工艺为最佳成形工艺方案.文中简要介绍了5×l04KN液压机上实现新工艺时模具结构特性.经工艺试验确定了变形温度约为450℃.应变速率为1.O×l0-3～6.3×10-3s-1,及较佳的坯料形状、尺寸及润滑剂.分析了该模锻件产生缺陷的原因和消除缺陷的方法.用新工艺研制的锻件冶金质量符合AIR3385、Z9-J冶-324、Z9-J冶-325技术条件要求,并且锻件的冶金质量有所提高,满足了生产要求.     

Effects of strain rates on dynamic deformation behavior of Cu-20Ag alloy

Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electri-cal conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a complex service condition,which widely exists in the field of national defense,military and industrial application.Therefore,the dynamic deformation behavior of the Cu-20Ag alloy was inves-tigated by Split Hopkinson Pressure Bar (SHPB) with the strain rates of 1000-25000 s-1,high-speed hydraulic servo material testing machine with the strain rates of 1-500 s-1.The effect of strain rate on flow stress and adiabatic shear sensitivity was analyzed.The results show that the increase of strain rate will increase the flow stress and critical strain,that is to say,the increase of strain rate will reduce the adiabatic shear sensitivity of the Cu-20Ag alloy.The Cu-Ag interface has obvious orientation relationship with (111)Cu//(111)Ag;((1)11)Cu//((1)11)Ag;((2)00) Cu//((2)00)Ag and[0(1)1]Cu//[0(1)1]Ag with the increase of strain rate.The increase of strain rate promotes the precipitation of Ag and increases the number of interfaces in the microstructure,which hinders the movement of dislocations and improves the stress and yield strength of the Cu-20Ag alloy.The concentration and distribution density of dislocations and the precipitation of Ag were the main reasons improve the flow stress and yield strength of the Cu-20Ag alloy.     

Isothermal oxidation behaviour of EB-PVD MCrAlY bond coat

The isothermal oxidation behaviour of EB-PVD NiCoCrAlY bond coat on nickel based superalloy at different treatment conditions were studied at 1100 °C up to 100 h. The reaction products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDS). It is found that after 10 h oxidation, while a protective alumina layer was developed on pre-oxidized specimens, a mixed oxide layer was observed on non-pre-oxidized specimens. Only after 50 h, spallation was observed on pre-oxidized specimens but did occur after 10 h for a non-pre-oxidized one, in both cases it is believed that the diffusion of the substrate element Ti to the surface of the bond coat deteriorates the adhesion of protective oxide to the bond coat and hence leads to spallation. Oxide rich in Ti was found to be located on the top of column grains rather than in the column grain boundaries.     

Plasma oxidation of Cu-Al alloy

Selective oxidation of Cu-1.0 wt % Al alloy was found to be achieved by using microwave plasma at 1073 K in a mixed gas of 10 % 0₂ and 90 % N₂ at a total pressure of 2 torr (∼266.644 Pa). The selective oxidation was confirmed by electron diffraction analysis of aluminium oxide particles, microstructural observations and hardness measurements of the internal oxidation layer. Electrical conductivity and the thermal expansion coefficient of the oxidized specimens were measured. The morphology and distribution of the aluminium oxide particles formed in the oxidized alloy is also discussed.     

Low cycle fatigue behavior of a eutectic 80Au/20Sn solder alloy

The eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging. In this study, low cycle fatigue behavior of a eutectic 80Au/20Sn solder alloy is reported. The 80Au/20Sn solder shows a quasi-static fracture characteristic at high strain rates, and then gradually transforms from a transgranular fracture (dominated by fatigue damage) to intergranular fracture (dominated by creep damage) at low strain rates with increasing temperature. Coffin-Manson and Morrow models are proposed to evaluate the low cycle fatigue behavior of the 80Au/20Sn solder. Besides, the 80Au/20Sn solder has enhanced fatigue resistance compared to the 63Sn/37Pb solder.     

Isothermal tensile deformation behaviors and fracture mechanism of Ti-26Al-20Nb-0,5Mo alloy at different phase regions

In this paper, the microstructure evolution, the deformation behavior and the fracture mechanism of the Ti-26Al-20Nb-0.5Mo alloy have been systematically investigated during tensile test. Results show that increase in tensile temperature leads to decrease in strength and increase in ductility. Under the deformation temperature of room temperature and 600 °C, there were no change in the microstructure of the samples, and the movement of dislocations plays a very important role. With increase of deformation temperature, the spheroidization degrees of the lamellar orthorhombic phase increases and the volume fraction of that decreases. Particularly the deformation temperature rising to 950 °C, the morphology of some equiaxed α₂ phases had been flattened into an ellipsoidal shape and the lamellar orthorhombic phase had been spheroidized completely during the deformation process. The deformation mechanism was mainly based on merged of grains and grown at this moment. Moreover, the fracture changes from brittle fracture to ductile fracture with increase of deformation temperature. At the tensile temperatures of 750 °C and 950 °C, the dimples around the holes are very different, and the fractographs are wave feature and fish scale features, respectively. The reason for this feature is mainly related to the spheroidization degree of the lamellar during the tensile deformation process.     

La对Ni-Cr-W-Mo耐热合金1173K恒温氧化行为的影响

研究了不同La含量Ni-Cr-W-Mo耐热合金的1173 K恒温氧化行为.结果表明:La能明显提高合金的抗氧化能力.不同La含量合金的抗氧化性能从劣到优依次为:La含量为0%、0.048%、0.026%、0.087%.添加超过0.026%的合金由于析出La化合物,使La的固溶量未呈线性增加,而在0.048%处出现拐点.氧化中由于La化物不参与氧化,因此合金的抗氧化能力主要取决于La在合金中的实际固溶量,固溶的La形成LaCrO3是La提高合金抗氧化能力的主要原因.LaCrO3在氧化物晶界处的偏聚阻碍了Cr3+的扩散,并可作为MnCr2O4异制形核的核心,促进细小的MnCr2O4生成并弥散分布于Cr2O3之间,形成混合氧化膜,提高了氧化膜的粘附性,亦成为提高抗氧化能力的因素.     

Improving high-temperature oxidation behavior by modifying Al and Co content in Al-Co-Cr-Fe-Ni high-entropy alloy

Composition modification was introduced to improve the oxidation resistance by varying Al and excluding Co from the Al-Co-Cr-Fe-Ni system. Since adjusting the composition shifted the valence electron concentration(VEC) of the alloys, the dual-phase structure of the alloys is expected to be more stable. At low temperatures(T < 1273 K), the alloys formed mixed oxide products. As oxidation temperature increased,only Cr₂O₃ or Al₂O₃ dominated the alloy’s...     

Surface characteristics and electrochemical corrosion behavior of a pre-anodized microarc oxidation coating on titanium alloy

A porous bioactive titania coating on biomedical β titanium alloy was prepared by pre-anodization followed by micro arc oxidation technology. The effects of pre-anodization on the phase constituent, morphology and electrochemical corrosion behavior of the microarc oxidation coating were investigated. The results show that pre-anodization has less influence on the phase constituent and the surface morphology of the microarc oxidation coating, but improves the inner layer density of the microarc oxidation coating. The decrease of plasma discharge strength due to the presence of the pre-anodized oxide film contributes to the formation of the compact inner layer. The pre-anodized microarc oxidation coating effectively inhibits the penetration of the electrolyte in 0.9% NaCl solution and thus increases the corrosion resistance of the coated titanium alloy in physiological solution.     

Influence of alloy additions on oxidation

Abstract

Some of the important principles of alloy oxidation are discussed, with emphasis on the formation of protective Cr₂O₃, Al₂O₃, and SiO₂ scales on iron and nickel base alloys. The competition between internal and external oxidation is considered and it is shown how establishment of the protective layer is influenced by various parameters, including alloy interdiffusion coefficient, oxygen solubility and diffusivity in the alloy, and the relative growth rates of the various oxides. The importance of the transient stage of oxidation is emphasised, with particular reference to the population densities of the initial nuclei of the protective oxide and the rates of growth and coalescence of these particles to develop the healing barrier layer. Consideration is given to the effectiveness of the protective scales in service, with respect to transport processes and mechanical integrity. The influence of the minor alloying elements, manganese, titanium, aluminium, silicon, molybdenum, and niobium, on oxidation of Cr₂O₃ forming alloys is discussed.

MST/1017     

Cyclic oxidation of Haynes 230 alloy

The cyclic oxidation of Haynes 230 alloy (Ni-Cr-W-Mo alloy) was investigated in air at three different temperatures, 871, 982 and 1093 °C. Studies indicated that during cyclic oxidation, protective scales formed which were predominantly Cr₂O₃, with Kirkendall voids formed both at the scale/alloy interface and grain boundaries. Intergranular oxides were observed at temperatures above 982 °C while internal oxide particles were found above 1093 °C. Both intergranular and internal oxides were identified as aluminium oxide. A 50 m chromium-depleted zone developed after 70 h exposure at 1093 °C and was accompanied by disastrous scale spalling. The lowest chromium concentration within the depleted zone was 14 wt% which still provided a sufficient supply of chromium for development of a continuous Cr₂O₃ rich scale. Decarburization was observed at the higher temperature of 1093 °C, and a carbide-free zone developed. Also, it was found that Haynes 230 is subject to a sensitization process. At the lower exposure temperature of 871 °C, large amounts of chromium carbide formed preferentially at the grain boundaries. While at the surface region chromium carbide precipitation occurred at the twin boundaries.     

Ti-60钛合金电弧离子镀Ti-Al-(Cr)防护涂层的循环氧化行为

研究了Ti-60钛合金及Ti-48Al和Ti-48Al-12Cr(原子数分数,%)两种涂层在800℃的循环氧化行为.实验发现Ti-60钛合金基体在800℃氧化严重,氧化层发生了明显剥落.而两种涂层在800℃均能有效地保护Ti-60钛合金基体.在循环氧化过程中Ti-48Al-12Cr涂层增重明显小于Ti-48Al涂层,表现出更好的抗循环氧化能力.