Dynamic recrystallization behavior of burn resistant titanium alloy Ti-25V-15Cr-0.2Si

Dynamic recrystallization (DRX) behavior in β phase region for the burn resistant titanium alloy Ti?25V?15Cr?0.2Si was investigated with a compression test in the temperature range of 950?1100 °C and the strain rate of 0.001?1 s?1. The results show that deformation mechanism of this alloy in hot deformation is dominated by DRX, and new grains of DRX are evolved by bulging nucleation mechanism as a predominant mechanism. DRX occurs more easily with the decrease of strain rate and the increase of deformation temperature. Grain refinement is achieved due to DRX during the hot deformation at strain rate range of 0.01?0.1 s?1 and temperature range of 950?1050 °C. DRX grain coarsening is observed for the alloy deformed at the higher temperatures of 1100 °C and the lower strain rates of 0.001 s?1. Finally, in order to determine the recrystallized fraction and DRX grain size under different deformation conditions, the prediction models of recrystallization kinetics and recrystallized grain sizes were established.

Double Glow Plasma Surface Alloyed Burn-resistant Titanium Alloy

Conventional titanium alloy may be ignited and burnt under high temperature, high pressure and high gas flow velocity condition. In order to avoid this problem, we have developed a new kind of burn-resistant titanium alloy—double glow plasma surface alloying burn-resistant titanium alloy. Alloying element Cr , Mo, Cu are induced into the TJ-6A1-4V and Ti-6.5Al-0.3Mo-l.5Zr-0.25Si substrates according to double glow discharge phenomenon, Ti-Cr ,Ti-Mo, Ti-Cu binary burn-resistant alloy layers are formed on the surface of Ti-6Al-4V and Ti-6.5Al-0.3Mo-l.5Zr-0.25Si alloys. The depth of the surface burn-resistant alloy layer can reach to above 200 microns and alloying element concentration can reach 90%. Burn-resistant property experiments reveal that if Cr concentration reach to 14%, Cu concentration reach to 12%, Mo concentration reach to 10% in the alloying layers, ignition and burn of titanium alloy can be effectively avoided.

APPLICATION OF CBN WHEEL IN CONSTRAININGWORKPIECE BURNING DURING CREEP FEEDGRINDING OF TITANIUM ALLOY

The burning mechanism during creep feed grinding of titanium alloy with SiC wheel is stud- ied. A CBN intermittent creep feed grinding technology combining the advantages of CBN, intermittent grinding and creep feed grinding is recommended. The results show that the intermittent CBN wheel has a bright future in resolving the problem of workpiece burning during creep feed grinding of titanium al- loys

High Tem perature Defor mation Mechanism of Ti-40 Burn Resistant Titaniu m Alloy As-annealing

Ti 40 alloy is a single β phase burn resistant titanium alloy. Its high temperature deformation mechanism and stress strain ( σ ε ) curves were studied by Gleeble 1500 thermal simulator. The results suggest that there are a bit abrupt flow stress drops followed by steady state in Ti 40 alloy as annealing. The magnitude of the flow stress drop increases with strain rate and decreases with temperature. Its deformation activation energies are 174 kJ/mol for 650～850℃ and 276.7 kJ/mol for 950～1000℃, which are close to or bigger than the values for self and solute lattice diffusion in pure β titanium, thereby, the deformation mechanism at temperature range is controlled by lattice diffusion for 650～850℃, or mainly controlled by dynamic recrystallization for 950～1000℃.

Burn-resistant behavior and mechanism of Ti14 alloy

The direct-current simulation burning method was used to investigate the burn-resistant behavior of Ti14 titanium alloy.The results show that Ti14 alloy exhibits a better burn resistance than TC4 alloy（Ti-6A1-4V）.Cu is observed to preferentially migrate to the surface of Ti14 alloy during the burning reaction,and the burned product contains Cu,Cu2O,and TiO2.An oxide layer mainly comprising loose TiO2 is observed beneath the burned product.Meanwhile,Ti2Cu precipitates at grain boundaries near the interface of the oxide layer,preventing the contact between O2 and Ti and forming a rapid diffusion layer near the matrix interface.Consequently,a multiple-layer structure with a Cu-enriched layer（burned product）/Cu-lean layer（oxide layer）/Cu-enriched layer（rapid diffusion layer） configuration is formed in the burn heat-affected zone of Ti14 alloy;this multiple-layer structure is beneficial for preventing O2 diffusion.Furthermore,although A1 can migrate to form A12O3 on the surface of TC4 alloy,the burn-resistant ability of TC4 is unimproved because the Al2O3 is discontinuous and not present in sufficient quantity.

HIGH TEMPERATURE DEFORMATION MECHANISM AND CONSTITUTIVE EQUATION OF Ti-40 BUREN RESISTANT TITANIUM ALLOY

Ti - 40 alloy is a single β phase burn resistant titanium alloy.Its high temperature deformation mech- anism is studied and its stress - strain curves are examined he use of Gleeble - 1500 thermal -simulator. The results reveal that there are abrupt flow stress drops followed b steady state.The magnitude of the flow stress drop increases with strain rote and decreases with temperature.Deformation activation energy, Q, is 247. 5 KJ/mol. The deformation mechanism of Ti - 40 alloy is controlled by the lattice diffusion Its constitutive equation is set up, i. e.

Effect of size and distribution of titanium carbide on microstructure and mechanical properties of Ti-25V-15Cr-2Al-0.2C-0.2Si alloy

The effect of size and distribution of titanium carbide on the microstructure and mechanical properties of non-burning β titanium alloy Ti-25V-15Cr-2Al-0.2C-0.2Si (mass fraction, %) was investigated. The microstructure of the heat-treated and exposed alloy was studied using optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). It is found that carbides with finer size and more uniform distribution can suppress the formation of α precipitates more effectively, and can especially decrease the amount of grain boundary α precipitates after long-term exposure at 540℃ (the expected application temperature). Thus, significant improvement in thermal stability can be achieved by refining carbide particles in the matrix of the alloy.

Thermodynamic Analysis of Burning Resistivity of Ti-Cr-V-Mo Alloys

Burning resistivities of the Ti Cr V Mo alloys were investigated by means of their adiabatic flame temperatures. Calculated results show that the adiabatic flame temperature of the Ti Cr V Mo alloys is lower than that of the Ti Cr V alloys, most probably due to that the gas products of molybdenum oxide can be easily formed and the sublimation of more oxides leads to the reduction of T af . Therefore, the Ti Cr V Mo alloys would have better burning resistivity and their optimal composition is presented.

激光熔覆TF550阻燃钛合金的组织和性能研究

研究了工艺参数对激光熔覆TF550阻燃钛合金成形质量的影响,以及微观组织和力学性能演变规律。结果表明,对试样成形的影响因素主次为激光功率>扫描速度>送粉率。不同激光功率下的激光熔覆TF550阻燃钛合金块体试样顶部及底部均由等轴Prior-β晶粒组成,中间区域为粗大的柱状Prior-β晶粒。随着激光功率的增大,各区域的晶粒尺寸也随之增大。激光熔覆TF550阻燃钛合金试样的显微组织主要由鸡爪状的TiC相、点状的Ti_(5)Si_(3)以及针状的α组成。激光熔覆TF550试样的平均显微硬度均呈现出沉积区>热影响区>基材的规律。激光熔覆TF550试样水平方向的抗拉强度以及屈服强度均略高于锻件,但伸长率仅为锻件的72%,其断口形貌呈现出混合断裂的特征。

普通电渣炉的全密闭气氛改造及其对典型钢种的影响

随着电渣钢品质的不断提升,普通电渣炉亟须进行全密闭气氛保护的升级改造,从而解决电渣重熔过程元素烧损、增氧、增氢、氢气孔等问题。采用新型的电渣炉气氛改造技术,分别用5 t和2 t电渣炉对GCr15SiMn轴承钢和GH2132高温合金进行传统气氛保护电渣炉和新型电渣炉的对比试验。冶炼过程中实现了结晶器内氧分压低至1×10^(-6)。试验数据显示,传统气氛保护电渣炉冶炼下,GH2132中Ti收得率低,仅为88%;GCr15SiMn轴承钢电渣重熔过程中增w[O]量大,可达5×10^(-6)。而在新型气氛保护改造中,GH2132中的Ti收得率高达96%;重熔过程轴承钢增w[O]控制在3×10^(-6)以内,电渣锭中w[O]稳定控制在10×10^(-6)以内,其电渣锭效果媲美气保电渣炉。以上炉内氧分压和电渣锭检测结果表明,电渣炉气氛改造后,可有效解决传统气氛保护改造技术下,往复的热浪涌出和负压吸气导致的结晶器内氩气保护不稳定,从而造成电极表面氧化,氧化皮掉入渣中引起的熔渣氧势升高和电渣锭增氧的问题;尤其对于GH2132高Ti低Al型高温合金,普通电渣炉加入脱氧剂Al条件下,无法避免Ti的烧损,只能导致电渣锭增Al。

阻燃钛合金的研究和发展

综述了阻燃钛合金的阻燃机理、阻燃合金体系和阻燃性能评价方法,介绍了研究现状及发展趋势,并对我国阻燃钛合金的发展提出了一些建议。

摩擦点火Ti-V-Cr阻燃钛合金燃烧产物的组织特征

采用摩擦氧浓度实验方法,结合原位观察、扫描电镜、能谱仪和X一射线衍射分析,系统研究Ti-V-Cr阻燃钛合金燃烧产物的微观组织形貌、燃烧反应过程的合金元素分布规律及微观机理.结果表明:Ti-V-Cr阻燃钛合金燃烧过程发出闪亮耀眼的白光,具有典型金属燃烧的火焰特征.燃烧产物主要有TiO_2,V_2O_5和Cr_2O_3三种氧化物,该混合氧化物以分散颗粒和致密连续体存在.分散颗粒为规则的球形;致密连续燃烧产物的微观组织具有分区特征,从合金基体至燃烧表面依次为过渡区、热影响区、熔凝区和燃烧区.其中,过渡区存在一些微小的颗粒状凸起,且有一定方向性;热影响区中形成大量V基固溶体相和少量的Ti基固溶体相,V基固溶体相上存在Ti的含量远高于基体的针状析出物;熔凝区中,大量的Ti基固溶体中存在少量的V基固溶体;燃烧区主要为Ti,V和Cr的氧化物混合物.热影响区的V基固溶体相降低了Ti元素向熔凝区的迁移速率,减慢了燃烧区Ti与O的优先反应;燃烧区形成的TiO_2,V_2O_5和Cr_2O_3混合氧化物和熔凝区O在Ti中大量固溶共同终止了O向合金基体的继续扩散,从而使Ti-V-Cr阻燃钛合金表现出优异的阻燃功能性.

合金元素Cr对钛合金燃烧行为的影响

以直流电弧激发燃烧法（ＤＣＳＢ）点燃钛合金，探讨了合金元素Ｃｒ对钛合金燃烧行为的影响。结果表明：合金元素Ｃｒ含量高于１０％可改善钛合金的阻燃性能，大于１５％效果更明显，而ＴｉＣｒ二元合金不具有阻燃性能。原因在于：ＴｉＣｒ合金燃烧产物表面均开裂多孔，Ｔｉ（＜１０％）Ｃｒ合金的燃烧产物与基体的界面亦如此，不可能阻止氧向基体内扩散；而Ｔｉ（＞１０％）Ｃｒ合金的燃烧产物与基体的界面富积Ｃｒ，氧化物比较致密，可阻止氧向基体内扩散，降低燃烧速度。ＴｉＣｒ合金的燃烧产物是ＴｉＯ２，ＴｉＯ和ＴｉＣｒＯ３。

Ti40和Alloy C在燃烧过程中的氧化界面分析

采用直流电弧激发燃烧法 (DCSB法 )测试 Ti4 0 ,Alloy C和 TC4合金在 3种气氛条件下的相对质量燃烧速度。结果表明 :与 TC4合金相比 ,Ti4 0与 Alloy C均具有较好的阻燃性能 ,用氮气来稀释空气能够降低钛合金的燃烧速率。用扫描电镜 (SEM)与 X射线能谱 (EDAX)观察分析了合金的燃烧产物、界面与基体 ,发现 :当 Ti4 0和 Alloy C燃烧时 ,V优先迁移至表层 ,因而燃烧区表层氧化层为富 V贫 Cr,而燃烧产物与基体界面附近氧化层则为富 Cr贫 V。Ti4 0与 Alloy C界面的富 Cr贫 V混合氧化层非常致密 ,既可抑制氧扩散入基体 ,又可阻碍基体中的 V扩散进入燃烧区。TC4燃烧时 ,虽然 Al优先迁移至表面与氧反应生成 Al2 O3,但该氧化层不连续不能有效降低燃烧速度 ,Cr。

钛合金在Ar与O_(2)气氛中的燃烧行为

以 DCSB法点燃钛合金 ,研究钛合金在 Ar气与 O2 气氛中的燃烧行为 ,分析常规钛合金一旦着火应采用什么方法灭火。研究结果表明 :钛可在富氧环境中燃烧 ;钛的燃烧可用 Ar气灭火 ;钛在富氧环境中燃烧的产物及燃烧产物与基体的界面均不致密 。

航空用钛合金阻燃技术

综述了航空用钛合金的阻燃技术和阻燃机理,介绍了国内外阻燃技术的研究和应用状况。

界面在钛合金燃烧过程中的作用

高推重比航空发动机中的钛火在燃烧过程中燃烧界面对钛合金燃烧行为有重要影响。研究结果表明，钛合金燃烧产物与空气的界面及产物内部因膨胀系数、Ｐ－Ｂ比不同等原因，均严重开裂、多孔，不能阻止燃烧的持续进行。纯钛和ＴＣ４合金燃烧产物与基体的界面也如此，而Ｔｉ４０阻燃钛合金的燃烧产物与基体的界面致密，界面产物是稳定的具有保护作用的Ｃｒ２Ｏ３，可阻止空气中可燃气体氧向基体内扩散，降低合金的燃烧速度。

Ti-Cr-V与Ti-Cr-Mo合金阻燃机理热力学分析

根据绝热条件下体系平衡时总自由焓最小和焓恒定原理，计算了不同环境温度下钛合金的绝热燃烧温度。计算结果从热力学的角度揭示了铬、钒、钼等元素阻止合金燃烧蔓延的效应和机理。

双辉等离子表面合金化技术形成表面阻燃钛合金的展望

本文综述了钛及钛合金燃烧的原因、现有的阻燃合金及阻燃机理,对利用双层辉光等离子渗金属表面合金化技术在钛及钛合金表面渗入Cr、Cu、Nb合金元素,形成表面阻燃钛合金的前景进行了展望。

SiC长纤维增强钛合金基复合材料的界面研究

研究了SiC/TC4和SiC/Ti40复合材料在不同热处理态下的界面行为。结果表明,SiC/Ti40复合材料相邻两纤维间存在TiC析出物,在1 000℃处理后,TiC析出物消失;2种复合材料界面反应厚度随处理温度升高和时间延长而增大;SCS-6 SiC/TC4和SiC/Ti40复合材料界面产物均为Ti5Si3。