Mechanical properties and microstructure of Ti-6Al-4V compacts by metal injection molding

Ti-6Al-4V compacts were fabricated by metal injection molding(MIM). Influence of vacuum sintering time on mechanical properties and microstructure of the sintered compacts at 1 260 ℃ were investigated. The experimental results show that the compacts sintered at 1 260 ℃ for 3 -6 h, which was made from hydrogenation-dehydrogenation(HDH) powder(average particles size is 45 μm), have a relative density of 95.6%- 96.7%, ultimate tensile strength of 648 - 686MPa and 0.2% yield strength of 526 - 615MPa; but a lower elongation(＜4%) and that the compacts sintered at 1 260 ℃ for 2 - 6 h, which was made from 90% gas-atomized powder(average particles size is 32.5 μm) and 10 % HDH powder, have higher relative density(＞95 %), ultimate tensile strength of 800 -848MPa,0.2% yield strength of 712 - 762MPa and high elongation (7.4%- 9.5%). When the sintering time is increased,porosity decreases and microstructure of sintered products changes from equiaxed to typical Widmanstatten, the average sizes of prior β grains, α colonies and α phase thickness in the β grains increase accordingly. After HIP treatment,pores obviously become less, microstructure of alloy is refined and mechanical properties are greatly improved.     

钛合金表面声电沉积／碱热处理法制备HA涂层研究

为了使钛合金（Ti-6Al-4V）具有生物活性，可在其表面施加生物活性羟基磷灰石（HA）涂层。对比了声电沉积法和碱热处理法实验结果，采用扫描电镜（SEM）、X射线衍射仪（XRD）、电子能谱（EDS）、傅立叶红外透射光谱（FTIR）以及划痕测试等进行了分析。结果表明，直接采用声电沉积法在钛合金表面制备的羟基磷灰石涂层，经热处理后存在龟裂剥落现象；通过碱热处理法，对钛合金基体表面进行预处理，然后，借助声电沉积法，在钛金属表面沉积了透钙磷石涂层，经热碱液处理转变成的羟基磷灰石涂层，涂层完整，未出现剥落。经进一步高温烧结处理，所制涂层仍呈片状形貌，其由部分含钠的羟基磷灰石组成，而且HA涂层破坏的临界载荷未烧结前的4．365N提高至烧结后的8．175N。     

The corrosion and corrosion-wear behaviour of plasma nitrided 17-4PH precipitation hardening stainless steel

Plasma surface nitriding of 17-4 PH martensitic precipitation hardening stainless steels was conducted at 350 °C, 420 °C and 500 °C for 10 h using a DC plasma nitriding unit, and the surface properties of the plasma surface engineered samples were systematically evaluated. Experimental results have shown that the surface properties of the plasma nitrided layers in terms of hardness, wear resistance, corrosion behaviour and corrosion-wear resistance are highly process condition dependent, and it is feasible to provide considerable improvement in wear, corrosion and corrosion-wear resistance of 17-4PH steel using optimised plasma treatment conditions. All three treatments can effectively improve the surface hardness and the sliding wear resistance under unlubricated conditions; high temperature (420 °C and 500 °C) treated materials revealed improved corrosion and corrosion-wear properties due to the formation of surface compound layers.     

电沉积-烧结制备Co3O4锂离子电池负极及电性能

摘要：采用电沉积一烧结方法制备Co3O4锂离子电池负极。X射线衍射XRD分析表明，电沉积的物质是Co(OH)2相，300℃烧结后均转变为Co3O4相。扫描电镜SEM观察发现获得的Co3O4具有花瓣形貌，其花瓣厚度约20nm。在300℃分别烧结30、45、60min制备的Co3O4组装的Co3O4／Li电池，在充放电循环中的首次嵌锂比容量分别为1361．7、1457．6和1345．0mAh／g，首次脱锂比容量分别为757．7、905.0和794．8mAh／g,10次循环后，脱锂比容量分别上升到815．5、969．0和890．1mAh／g。     

Anti-oxidation mechanism of SiC-B4C-C composites

Mixture of green petroleum coke, B4 C and SiC together with short carbon fiber were employed as starting materials, the mixture was press formed without any binder after grinding, dense and homogeneous binderless SiC-B4 C-C（carbon/ceramic） composites were then obtained after sintering. Composites thus prepared possess excellent anti-oxidation property, that is, mass loss less than IG within the temperature range from 900 to 1 100 ℃ for 10 h. Anti-oxidation mechanism was also discussed from the viewpoint of thermodynamics, excellent anti-oxidation property of materials thus prepared can be discribed to 1） solid SiO2 formed from SiC, which restrains the filtering of oxygen and simultaneously, its volume expansion brought about by the reaction takes roles both walling up the original pores and making the material more compact; 2） liquid B2O3 from the reaction of B4C not only makes the combination with C, B4 C and SiC tighter through forming solid solution, but also effect of reaction SiC（s）＋2CO（g） =SiO2 （s）＋3C（s） is an expansive process, which improves the microstructure of the material.     

X70管线钢在近中性及高pH值溶液中的电化学行为和SCC敏感性

采用动电位极化曲线测试法研究了温度、通气条件和pH值对X70管线钢在NS4溶液和0.5 mol/LNa2CO3 1 mol/L NaHCO3溶液中的电化学极化行为的影响,并用慢应变速率试验(SSRT)研究了X70管线钢在这些溶液中的应力腐蚀破裂(SCC)敏感性。结果表明,X70管线钢在NS4溶液中不出现活化—钝化转变区,随外加电位负移,SCC敏感性增加,表现出氢致破裂(HIC)的特征;在0.5 mol/L Na2CO3 1 mol/L NaHCO3高pH值溶液中出现活化—钝化转变区,在阴极极化区,也表现出氢致破裂(HIC)的特征,但在阳极极化区,发生的是阳极溶解型应力腐蚀破裂(ADSCC)。     

电子束局部热处理对TC4合金接头疲劳性能影响

通过低周轴向应变疲劳试验,研究了电子束局部热处理对TC4钛合金接头疲劳性能的影响.结果表明,电子束局部热处理TC4钛合金接头在疲劳过程中存在一定的软化行为;在一定的载荷条件下,与焊后未热处理状态相比,经过电子束局部热处理后,TC4钛合金电子束焊接接头的疲劳寿命可以提高30%以上.     

锆-4合金低周疲劳断口裂纹扩展能量及分形特征研究

对锆-4合金低周疲劳裂纹扩展过程进行了探索性的研究。通过分析锆-4合金低周疲劳断口在裂纹扩展方向上能量及分形维数变化趋势，发现锆-4合金动态裂纹扩展中扩展期由3个阶段组成，每一阶段的能量和分形维数都不同。A-B段的能量最小，归一化值为0-0．0156，A-B段的分形维数居中，在工工方向均值为2．2796，标准差为0．0277，在LH方向均值为2．4516，标准差为0．0592。D-E段能量远大于A-B段，归一化值为0．8754～0．9652，但分形维数最小，LL方向均值为2．2214，标准差为0．0131，LH方向均值为2．3477，标准差为0．0550。F-H（或G-H）段能量最大，归一化值达到1，同时分形维数也达到最大，LL方向均值为2．3414，标准差为0．0704，LH方向均值为2．5398，标准差为0．0263。虽后，根据二次电子成像原理以及锆-4合金低周疲劳断口的形貌特征对此现象进行了初步分析。     

Numerical simulation on forging process of TC4 alloy mounting parts

1Introduction The TC4alloy mounting part is an important part of aeronautic engine.Currently,these mounting parts are mainly manufactured by metal cutting,which is expensive and requires a lot of manufacturing time.Furthermore,in this way the forging flow…     

Effect of some ternary additions on the sulfidation of Ni-Mo alloys

Five ternary additions, Cr, Ti, Mn, V, and Al were studied at equi-atomicpercent levels (17 a/o) for their effect on the sulfidation behavior of Ni-19a/o Mo (28–30 w/o) over the range of 600–800°C in 0.01 atm S₂. Al was by far the most effective addition. A linear decrease in log k_p vs. Al content was observed up to 7.5w/o Al, beyond which no further change was observed. All alloys followed the parabolic rate law. Arrhenius plots gave activation energies of 36.9–41.2 Kcal/mol for alloys containing Ti, Cr, Mn, and V, whereas the activation energies for Al-containing alloys were 47.2 Kcal/mol, indicating that a different diffusion process was involved. Complex scales were formed on all alloys, consisting of an outer layer of Nis_1+x and complex inner layers which depended upon alloy composition. Two alloys, those with Cr and Mn, formed intermediate layers of Cr₂S₃ and MnS, respectively, but these layers had little effect on the kinetics. MoS₂ was a constituent of the inner scales except for the alloys with Al. A ternary sulfide, Al_0.55Mo₂S₄ and Al₂S₃ were observed. The presence of the mixed sulfide was always associated with the low sulfidation rates. The formation of MoS₂ on alloys results in a different, less-protective behavior than for MoS₂ formed on pure Mo. This effect is due to the intercalation of Ni into MoS₂ in octahedral positions between the weakly bonded layers of covalently bonded sheets of trigonal prisms. The size of Al⁺³ is too small to be intercalated, and thus MoS₂ is destabilized by Al.