Interface microstructure evolution and bonding strength of TC11/c-TiA l bi-materials fabricated by laser powder deposition

Laser powder deposition was applied to fabricate the Ti-6.5Al-3.5Mo-1.5Zr-0.3Si （wt%）/Ti-47Al- 2Cr-2Nb-0.2W-0.15B （at%） bi-material system. The asdeposited TC11 alloy shows a basket-wave-like morphology while the as-deposited y-TiAl alloy consists of fully α2/γ lamellar microstructures. Regarding the thermal mismatch between TC11 and γ-TiAl during processing, the interface microstmcture evolution was concerned. The transformation pathway was illustrated. It is found that the content changes of Al elements and β-stabilizers Mo, Cr, and Nb are responsible for the evolution of microstructures at the interface. The fracture surfaces are located at the y-TiAl side. The bi-material shows a brittle-fracture manner, with the ultimate tensile strength of 560 MPa.

Effects of Chromium,Vanadium and Austenite Deformation on Transformation Behaviors of High-strength Spring Steels

The phase transformation behavior during continuous cooling of high-strength spring steels containing different amounts of Cr was studied. Furthermore, the effects of combining Cr with V as well as austenite deformation on the transformation kinetics were investigated in the method of dilatometry and metallography hardness. The re suits showed that, with the increase of Cr, the pearlite transformation field was enlarged, the ferrite transformation field was narrowed, and the entire phase field shifted to the right. With the addition of V, the start transformation temperature of undercooling austenite （Ar3） was gradually increased, but the ferrite and pearlite transformation fields were not affected. Besides, the minimum critical cooling rate of martensilic transformation was also reduced. In addition, the dynamic continuous cooling transformation （CCT） curve moves to the top left compared with the static CCT curve. The transformed microstructures showed that the addition of V and the deformation not only refined the overall transformed microstructures but also reduced the lamellar spacing of pearlite. The alloying elements Cr and V promoted the Vickers hardness. However, the effect of Cr on the Vickers hardness of martensite was stronger and the influence of V on that of pearlite was stronger. Moreover, the Vickers hardness affected by the austenite deformation was more complex and strongly depended on the transformed microstructures.

Determination of cut-off time of accelerated aging test under temperature stress for LED lamps

在LED灯具加速老化过程中,为获得最小截止时间,对其寿命进行快速预估,本文采用5阶滑动平均误差方法分析数据。选用同批次的16个样本,分别进行80℃和85℃应力条件下的加速老化。首先,采用e指数对光通维持率进行拟合,获得每个灯具的加速寿命,进而采用威布尔分布对加速寿命进行拟合,获得中位寿命。其次,采用平均滑动误差方法,可获取不同截止时间下中位寿命预估误差。结果表明:加速老化过程中,存在最小截止时间,该时间可通过滑动平均误差和截止时间的关系确定;当截止时间小于该值时,寿命预估不合理;寿命预估误差随截止时间增加而逐渐减小。对于该类LED灯具,80℃时最小截止时间为1104小时,寿命预估误差为1.15%;85℃时最小截止时间为936小时,寿命预估误差为1.24%。当寿命估计误差约为0.46%时,80℃和85℃对应的中位寿命分别为7310小时和4598小时。