A Newly Developed Wrought Ni-Fe-Cr-based Superalloy for Advanced Ultra-Supercritical Power Plant Applications Beyond 700 °C

doi:10.1007/s40195-015-0298-5

Abstract

Abstract:

Some existing wrought Ni-Cr-Co-based superalloys are being evaluated as the candidate materials for advanced ultra-supercritical power plant applications beyond 700 °C due to their high creep strength. But they are all prohibitively expensive due to the addition of Co, Mo and W. Here we developed a new Ni-Fe-Cr-based superalloy (named as HT700 alloy) with low cost and high strength. This paper reports the mechanical properties and fracture modes of HT700 alloy to support its high temperature applications and to understand prospective failure mechanism. Fractographic examinations indicate that the fracture modes shift with test condition change. In addition, the HT700 alloy has relatively stable microstructure at 750 °C. Compared with IN740 and GH2984 alloys, this new alloy has higher yield strength in the temperature range from room temperature to 800 °C. The creep life of this new alloy is much longer than that of the Ni-Fe-based superalloy GH2984. The results suggest that this new alloy is a promising material for advanced ultra-supercritical power plant applications beyond 700 °C.

Key words: Wrought Ni-Fe-Cr-based superalloy, Low cost, High strength, Fracture mode

Shuai Guan, Chuan-Yong Cui. A Newly Developed Wrought Ni-Fe-Cr-based Superalloy for Advanced Ultra-Supercritical Power Plant Applications Beyond 700 °C[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(9): 1083-1088.

Figures/Tables 8

Fig. 1 a Image of the HT700 alloy illustrating twin boundaries and MC carbides within the grains, b TEM morphology and SAED pattern of grain boundary precipitation.

Fig. 2 a Tensile engineering stress strain curves of HT700 alloy tested at room temperature, 700 and 800 °C, b comparison of tensile yield strength for HT700, IN740 and GH2984 alloys from room temperature to 800 °C.

Table 1 Microstructural parameters of HT700, GH2984 and IN740 alloys

	Content of Al + Ti (wt.%)	Grain size (μm)	γ′ content (%)
HT700	4.2	56	20
GH2984	1.1-1.7	65	6
IN740	2.3-2.7	200	13

Fig. 3 Typical fracture surfaces for tensile tests at room temperature a, b, 700 °C c, d. Note the fracture surface transformed from transgranular (room temperature) to predominantly transgranular but with small range intergranular area with grain boundary cracking.

Fig. 4 a Creep curves of HT700 alloy tested at 750 °C and 200 MPa, at 750 °C and 250 MPa and at 800 °C and 200 MPa; b LMP of HT700 alloy plotted as a function of stress, together with that of GH2984 alloy.

Table 2 Creep life and elongation of HT700 alloy tested at various conditions

Condition	Life (h)	Elongation (%)
750 °C/200 MPa	940	12
750 °C/250 MPa	215	16
800 °C/150 MPa	192	18
800 °C/200 MPa	122	10

Fig. 5 Typical fracture surfaces of the alloy crept at 750 °C/200 MPa a, c, 750 °C/250 MPa b, d.

Fig. 6 Typical γ′ phase of as-aged HT700 alloy a, HT700 alloy b after creep rupture tested at 750 °C/250 MPa, c HT700 alloy after creep rupture tested at 800 °C/150 MPa.

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