Ni-15Cr-6W-3Mo-2Al-2Ti变形高温合金的室温抗张强度、塑性和冲击性能,随着合金中Si含量的变化呈现马鞍型的变化,即在0.4—0.6％Si范围内出现一个低塑性、低拉伸强度和低冲击韧性区。造成这种现象的本质原因是由于Si含量变化改变了晶界碳化物沉淀析出顺序、析出类型、析出量和析出形态。该合金晶界碳化物析出可分为四个阶段:第一阶段,<0.1％Si时,只有单一的M_(23)C_6析出;第二阶段,>0.1％Si以后,除M_(23)C_6外,M_6C开始析出,一直到0.4％Si时增加2缓慢;第三阶段,0.4—0.6％Si时,M_6C大量析出逐渐取代M_(23)C_6;第四阶段,>0.6％Si以后,M_6C量占绝对优势,但增加幅度比第三阶段小得多。从晶界形态来看,第一、二、四阶段皆属不连续的链状形式,只有第三阶段晶界呈现连续膜状。因此,造成性能下降的原因不是因为析出M_6C,而是它的形态,当它以颗粒状分布在晶界上时是一个很好的强化相。第三阶段的不正常析出是性能下降的本质因素。本研究结果打破了只要镍基合金中MO+1/2>W>6％(重量百分比)就形成M_6C的经验判据,“Si”才是该合金碳化物沉淀析出过程的控制因素。本文还对比了冶炼工艺差别对碳化物析出过程的影响。
The tensile strength, ductility or impact value of a wrought nickel base super-alloy Ni-15Cr-6W-3Mo-2Al-2Ti depend markedly upon the silicon content of thealloy. On plotting these mechanical properties vs the silicon content which rangesfrom 0.1 to 0.89%, a saddle shown by the existence of a minimum at about 0.4-0.6% Si occurs. There is reason to believe that such a saddle behavior may be caus-ed by the variation of mechanical properties with the type, amount and morpho-logy of carbides as well as with the sequence of carbide precipitation in the alloyas influenced by its silicon content. Thus, the amount of M_6C and M_(23)C_6 precipi-tated along the grain boundaries would appear to proceed in four stages as follows: 1. For silicon content up to 0.1%, globular M_(23)C_6 may be the sole type ofcarbide formed; 2. In the range from 0.1 to 0.4% Si, besides M_(23)C_6, M_6C begins to appearand increases with increase of silicon content. The morphology of the carbidesseems to be different, however, being in a discontinuous, blocky form; 3. In the range from 0.4 to 0.6% Si, continuous films of M_6C were present.As might be expected, this type of carbide is very detrimental to the tensile andimpact properties at room temperature. The precipitation of M_(23)C_6 was slowed downor even suppressed; 4. In the range from 0.6 to 0.89% Si, M_6C may be altered to discontinuous,blocky form, whereas M_(23)C_6 may be very much limited. In conclusion, the detrimental effect of carbide is mainly associated with itsfilm-like morphology especially along the grain boundaries. Of course, carbides ingranular form are good strengtheners. According to prevailing view, criterion for the formation of either M_6C orM_(23)C_6 in nickel base superalloys would seem to be the relative Mo and W con-tents, e. g. if Mo+1/2W>6%, M_6C will be formed. Present work indicates that si-licon plays as equally important role in the formation of M_6C besides the Mo andW contents of the wrought nickel base superalloys.
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