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含Hf的镍基高温合金存在Ni_5Hf相,它是影响合金初熔的主要因素之一。当该相的量大于1.0v-%时,在加热示差热分析(DTA)曲线上的1135-1160℃处出现Ni_5Hf相的熔化峰。P.D法定向铸锭上、下端存在明显的Ni_5Hf偏析,因而对初熔的敏感性明显不同。Ni_5Hf相的初熔促进了共晶γ′和M_3B_2的熔化。低碳与无碳含Hf合金的初熔倾向更大,缓冷组织和固溶处理的升温速度对初熔是敏感的。高于3V-%的初熔量将会降低合金的持久强度,其断裂主要沿Ni_5Hf初熔区和共晶γ′之间的界面扩展。采用1150℃8h预处理能消除全部的Ni_5Hf相,有效地控制含Hf合金的初熔。
The Ni_5Hf phase exists in the Hf-containing Ni-based superalloy, which is one of the main factors affecting the initial melting of the alloy. When the amount of this phase is more than 1.0 v-%, a melting peak of the Ni_5Hf phase appears at 1135 to 1160 ° C on a thermogravimetric analysis (DTA) curve. P.D method orientation ingot, the bottom there is obvious Ni_5Hf segregation, and therefore the sensitivity of the initial melt significantly different. Initial melting of Ni_5Hf phase promotes the melting of eutectic γ ’and M_3B_2. The initial melting tendency of low-carbon and non-carbon-containing Hf alloy is greater, and the rate of temperature rise of slow cooling and solution treatment is sensitive to primary melting. Initial melting of more than 3V-% will reduce the long-term strength of the alloy, and its fracture mainly extends along the interface between Ni_5Hf primary melting zone and eutectic γ ’. Using 1150 ℃ 8h pretreatment can eliminate all Ni_5Hf phase, effectively control the initial melting of Hf-containing alloys.