Development of high creep-resistant TiAl-base alloys for directional solidification and measurements of their creep resistance using large-sized specimens

可以使用Ti-43 Al-3Si晶种合金的晶种来生长具有对齐的层状微观结构的Ti-47 Al合金锭。与Ti-47 Al合金类似，如果合金化不会导致基础合金的凝固路径发生任何显著变化，则基于该合金的多组分合金应该可以进行引晶。当确定合金元素和添加到基础Ti-47 Al合金中的每种元素的量时，修改基础合金的Al含量以使α/β主区边界的相对位置保持为二元系统中的相对位置。新合金的Al含量C_<AI>可使用以下等式计算。c_<Al>=47 + aX_<eq>+ bY_<eq>+ cZ_<eq>+...，其中a、B、c和X_<eq>、Y_<eq>、Z_<eq>分别是合金元素X、Y、Z的量和Al当量。当约46 &lt; c &lt;<Al>48时，在生长时使用Ti-43 Al-3Si晶种合金的晶种可以使层状微观结构沿着生长方向排列。 关于我们 在750℃和240 MPa的空气中，使用从定向凝固锭中切割的标距尺寸为30 mm长和6 mm直径的试样进行蠕变试验。结果表明，沿沿着方向排列片层边界不仅能降低二次蠕变速率，而且能降低一次蠕变应变。二元Ti-47 Al合金在蠕变条件下的二次蠕变速率为2.07 × 10 ~（-4）<-9>s ~<-1>（-1），这仍然与所报道的高合金化的先进TiAl基多晶合金的二次蠕变速率相当或更低，远高于四元和五元合金的二次蠕变速率。值得注意的是，添加少量的Si和过渡金属如Mo、W和Re显著提高了定向凝固的TiAl基合金锭的抗蠕变性。Ti-46 Al-0.5Si-0.5W和Ti-46 Al-0.5Si-0.5Mo合金定向凝固铸锭的抗氧化性与最常见的TiAl基合金之一Ti-48 Al-2Cr-2Nb相当。然而，添加3%的Nb显著提高了抗氧化性，而没有引起机械性能的任何显著变化。少

Ingots of Ti-47Al alloy with an aligned lamellar microstructure can be grown using a seed of the Ti-43Al-3Si seed alloy. Similarly to the Ti-47Al alloy, seeding should be possible for multi-component alloys based on this alloy if alloying may not cause any significant change in the solidification path of the base alloy. When the alloying elements and the amount of each element to be added to the base Ti-47Al alloy are determined, the Al content of the base alloy is modified to let the relative position of the α/β primary region boundary remain as that is in the binary system. The Al content of the new alloy, C_<AI> can be calculated using the following equation. c_<Al>=47 + aX_<eq> + bY_<eq> + cZ_<eq> +..., where a, b, c and X_<eq>, Y_<eq>, Z_<eq> are the amount and the Al-equivalent of alloying elements X, Y, Z, respectively. When approximately 46 < c_<Al> < 48, the lamellar microstructure can be aligned along the growth direction using a seed of the Ti-43Al-3Si seed alloy at a growth … More rate of 10mm/h.Creep tests were performed in air at 750℃ and 240MPa using specimens with a gauge size of 30 mm in length and 6 mm in diameter cut from directionally solidified ingots. It was found that not only the secondary creep rate but also primary creep strain were reduced by aligning the lamellar boundaries along the loading axis. The secondary creep rate of the binary Ti-47Al alloy under the creep condition is 2.07 x 10^<-9>s^<-1>, which is still comparable to or lower than that reported for the highly alloyed advanced TiAl-base polycrystalline alloys, is much higher than those for the quaternary and quinary alloys. It is of interest to note that the addition of a small amount of Si and transition metals such as Mo, W and Re dramatically increases creep resistance of directionally solidified ingots of TiAl-base alloys. The oxidation resistance of the directionally solidified ingots of Ti-46Al-0.5Si-0.5W and Ti-46Al-0.5Si-0.5Mo alloys is comparable to that of Ti-48Al-2Cr-2Nb, which is one of the most common TiAl-base alloys. However, adding 3% Nb significantly improves oxidation resistance without giving rise to any significant change in the mechanical properties. Less