半固态变形量对Ti14合金热稳定性的影响

研究新型阻燃钛合金Ti14(α+Ti2Cu)经不同变形量(45%～75%)半固态锻造后的热稳定性能,分析变形量对合金热稳定性能的影响。结果表明:变形量改变析出相的形态及晶粒尺寸,使合金具有不同的热稳定性能。随变形量的增加,Ti14合金热暴露后的强度呈先降低后升高的趋势,塑性有所改善。半固态变形量较小时(45%),合金晶粒粗大,Ti2Cu相呈长条状分布于晶界,高的强度取决于析出相强化作用;随变形量增大(75%),晶粒细化,Ti2Cu相呈颗粒状或短棒状弥散分布,产生细晶强化,使得强度和塑性都得到改善。断口分析表明:变形量较小,断口存在大量撕裂棱;变形量达到75%,断口以韧窝为主;表明析出相和晶粒尺寸共同决定Ti14合金的热稳定性能。     

Ti40合金热稳定性能的初步研究

研究了热处理制度和少量合金元素Si对β型阻燃钛合金Ti40热稳定性的影响.结果表明含0.2%Si的合金,固溶温度越高,热暴露后析出的Ti5Si3相越粗大,明显降低合金热稳定性能.820℃/0.5 h,WQ+600℃/5 h,AC热处理后,与无暴露相比,含0.2%Si的合金热暴露后析出的Ti5Si3相使合金塑性明显下降;与不含Si的合金相比,含0.2%Si的合金热稳定性能较差.     

β型Ti40阻燃钛合金高温长期作用的第二相及其对性能的影响

研究了β型Ti40阻燃钛合金高温长期作用的第二相及其对性能影响，Ti40合金高温长期作用后，从β相中析出Ti5Si3相和α相，采用常规锻造工艺不高于540℃热暴露100h,Ti5Si3相沿晶界不连续分布，降低合金热稳定性能，700℃热暴露100h，Ti5Si3相明显，大大降低合金热稳定性能，合金呈脆性沿晶界断裂，采用等温锻造工艺540℃热暴露100h，晶内析出粗大的Ti5Si3相和α相，热稳定性能严重降低，呈宏观脆性断裂，采用常规锻造工艺合适的热处理制度，540℃，100h,250MPa蠕变作用后Ti5Si3相沿晶界不连续分布，合金有较好的蠕变性能，若热处理工艺不当，合金中有大量粗大的棒状Ti5Si3相和α相析出，Ti5Si3 相沿晶界连续分布，合金的蠕变抗力明显降低，采用等温锻造工艺蠕变作用后，合金中析出大量粗大的α相，合金蠕变抗力也明显降低。     

Ti14合金半固态变形的晶界偏析行为

以新型阻燃钛合金Ti14(α+Ti2Cu)为对象,研究了合金在半固态条件下的晶界偏析行为.结果表明,Ti14半固态变形使得Cu元素在晶界偏聚,冷却后以Ti2Cu相偏析于晶界,偏聚和偏析过程与半固态变形温度具有较大的相关性;同时,提出了Ti2Cu相形核和析出长大动力学模式,并用非经典形核长大理论进行了解释.     

热暴露对Ti3Al/TC11双合金连接界面组织和拉伸性能的影响

对550℃热暴露50h的Ti3Al/TC11双合金拉伸试样用OM和SEM观察连接界面在近等温锻造、热处理和热暴露后的组织与断口形貌。结果表明:梯度热处理条件下,随着变形量的增加,试样热暴露后室温抗拉强度升高;连接界面上锻造形成的细针状α交织组织在热暴露期间发生分解、粗化,同时焊缝中析出更多细小的球状α/α2相。采用梯度热处理的双合金试样热暴露后强度稍高于经双重热处理的试样,双重热处理试样中Ti3Al基合金热影响区的α2相在热暴露期间发生长大。由于氧化造成表面微裂纹,使得试样直接热暴露性能低于毛坯热暴露性能。从拉伸断裂位置可以看出,断裂主要发生在Ti3Al基合金侧。     

Al元素对Ti40阻燃钛合金550℃热稳定性的影响

研究Ti-25V-15Cr-0.2Si和Ti-25V-15Cr-2Al-0.2Si两种阻燃钛合金在550℃热暴露不同时间后的力学性能，并应用光学显微镜、X射线衍射、透射电镜对合金组织进行分析。结果表明，Al元素使Ti40阻燃钛合金在550℃的热稳定性能显著降低；对相的分析表明，Al元素可促进合金中Ti5si3和α相的形成。在550℃热暴露200h条件下，出现明显的TiCr2有序相。降低组织的稳定性及使合金在热暴露过程中生成过多的第二相是Al元素降低合金热稳定性能的主要原因。     

半固态锻造Ti14合金的拉伸性能和组织演变特征(英文)

通过室温和高温拉伸性能测试,对比研究了Ti14合金经常规锻造(950℃)和半固态锻造(1000℃和1050℃)后试样在不同温度区间的宏观力学行为,分析了微观组织演变规律、断口微观形貌及断裂特征。结果表明:合金经半固态锻造后表现出高强度、低塑性的力学特征,随着半固态锻造温度的升高,合金力学性能下降。半固态锻造过程中组织的变化是引起力学性能差异的主要原因,而组织演变的主要特征是Ti2Cu析出相形态和分布的变化。随着半固态温度的升高,更多的液相在晶界析出,并在凝固过程中析出大量板条状Ti2Cu相,最终在晶界上形成偏析带组织。这种带状组织在拉伸过程中引发了解离断裂,导致了低塑性。此外,通过再结晶退火可以有效地细化半固态组织,改善强度性能。     

Y、Sn对Cu60Zr30Ti10合金非晶形成能力及性能的影响

采用铜模喷铸法制备了φ4 mm×80 mill的Cu60Zr30Ti10、(Cu60Zr30Ti10)98 Sn2和(Cu60Zr30Ti10)98Y2合金棒试样.用X射线衍射仪(XRD)和差式扫描量热仪(DSC)分析了三合金内部结构及热稳定性.结果表明:合金元素Y、Sn均能提高Cu60Zr30Ti10合金的非晶形成能力,但添加Y的效果更佳.所制备的φ4 mm(Cu60Zr30Ti10)98Y2合金棒为完全非晶结构,且其热稳定性高于另外两种合金;非晶态(Cu60Zr30Ti10)98Y2合金的显微硬度低于由晶相/非晶组成的(Cu60Zr30Ti10)98Sn2、Cu60Zr30Ti10合金,且在该系列合金中,随着析出晶相增多,合金显微硬度下降.     

退火和热暴露对Ti-22Al-25Nb/Ti60双合金焊接盘组织和力学性能的影响

对真空电子束焊接后的Ti-22Al-25Nb/Ti60双合金盘试样进行了退火处理和热暴露试验,采用OM、SEM和TEM观察了接头的显微组织。对不同状态下的双合金试样进行了室温拉伸试验,并观察了拉伸断口形貌。结果表明:退火和热暴露会促使焊接过程形成的亚稳相分解。与退火态相比,热暴露态焊缝熔合区亚稳β相和Ti60热影响区α'相分解程度增加,热暴露后Ti-22Al-25Nb合金热影响区有细小的O相析出。焊态下拉伸试样发生脆断,退火后双合金试样强度有较大提升,并有一定的拉伸塑性。热暴露后双合金试样强度进一步提高,拉伸塑性较退火态变化不大。     

激光冲击强化近α钛合金的热稳定性

采用激光冲击强化工艺对近α型Ti834高温合金进行了表面处理,研究了激光冲击前后合金在600℃×100h的热稳定性和微观组织特征,并采用扫描电镜法分析了合金在不同状态下的拉伸断口特征。结果表明,合金经毛坯热暴露后,强度略有提高,而塑性变化不大;而经试样热暴露后,合金强度略有降低,塑性降低幅度较大。激光冲击处理使试样热暴露后的合金强度提高,而塑性进一步降低。在激光冲击处理过程中,合金表面晶体缺陷的形成是导致合金塑性进一步降低的主要原因。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.