ZHENG Yunrong
,
WANG Luobao
,
LI Chenggong Institute of Aeronautical Naterials
,
Beijing
,
China. To whom correspondence should be addressed.
材料科学技术（英文）
Hf lowers the incipient melting temperature of superalloy. As carbon content in Hf-bearing alloy decreases, the incipient melting temperature drops furthey. PD ingots have stronger tendency to incipient melting than HRS ones. Even though in PD ingot, the sensitivities at both ends of the ingot are quite different. The melting of Ni_5Hf phase may be considered as one of the main factors affecting incipient melting. The more Ni_5Hf the alloy contains, the more serious the incipient melting becomes. The results of differential thermal analysis (DTA) have proved that the peak of 1135-1160℃ corresponds to the melting range or Ni_5Hf. By means of a pretreatment at 1150℃, 8h, Ni_5Hf phase can be eliminated in two ways: the reaction Ni_5Hf+γ(C)→MC_(2)+γ and solid solution, and therefore the final solid solution treatment can be carried out at 1260℃. This brings about a high homogenized structure and further increases the stress rupture properties of the alloy at 1040℃, 140 MPa.
关键词:
DS superalloy
,
null
,
null
,
null
,
null
,
null
CHEN Rongzhang
,
WANG Luobao
,
WANG Yuping Institute of Aeronautical Materials
,
Beijing
,
PRC.
材料科学技术（英文）
The microstructure changed markedly with increasing solution temperature, i.e eutectic γ' phases and coarse primary γ' phase are redissolved continuously into matrix, which was finished at 1250-1260℃, and more and finer γ' phases are reprecipitated. The grain boundary morphology changed gradually to "fine line" form. The dendritic segregation of elements decreased. With raising solution temperature the longitudinal stress-rupture life at high and intermediate temperature were enhanced, but the transversal stress-rupture life at intermediate temperature decreased obviously. The incipient melting temperature of DZ22 alloy was measured to be 1230-1240℃ and may be increased by homogenization at 1150℃. In this paper the principle of determining solution temperature of DS alloys was discussed. It was suggested that the solution temperature of alloy DZ22 selected at 1200-1210℃ is appropri- ate.
关键词:
directional solidification
,
null
,
null
,
null
