News

August 2015

Mechanical Behavior of Superalloys

The superalloys are ductile in nature however cobalt based superalloys have lower ductility as compare to iron-nickel and nickel based superalloys. The short period tensile ductility varies from 10% to maximum 70% but gamma’ hardened alloys have low ductility up to 40%. The Superalloys generally have dynamic moduli of elasticity in the limit of 207 GPa or 30 x 10(6) psi, however moduli of certain polycrystalline alloys varies from 172 to 241 GPa or 25 x 10(6) to 35to 10(6) psi at room temperature on the base of alloy configuration. The dynamic measurement of elasticity moduli at the elevated temperatures is essential as the static modulus is widely affected by high temperatures and gives minor reductions on the dynamic value at a general high temperature. The static modulus may fall up to 30% with increase in temperature from room to 871oC or1600oF. The short term tensile yield characteristics of gamma’ hardened alloys vary from 550 MPa or 80 ksi to 1380 MPa or 200 ksi at room temperature. The data depends on composition and treatment. The wrought superalloys have the maximum values with the maximum hardener content alloys providing the highest strength. Although, strength is a function of grain size and stored energy. The superalloys such as Inconel 718 or U630 can be forged for achieving extremely high yield strength. Solid solution hardened alloys like sheet Hastelloy X have smaller strength levels. The strength of superalloys varies from 690 MPa to 1520 Mpa or 100 ksi to 230 ksi at the room temperature with gamma’ hardened alloys in the high end range. The superalloys give increased yield strength from room temperature up to a temperature of 760oC or 1400oF and then decrease with further increase in temperature. It is unlike to alloys that cause regular drop in short yield strength with increase in temperature. The mechanical strengths normally do not exhibit this behavior. Alongside, tensile ductility decreases with nominal in the limit of 649oC to 760oC or 1200oF to 1400oF. The maximum tensile characteristics are observed in fine grain size wrought or powder metallurgy superalloys utilized in operations at the upper portion of the moderate temperature regime about 760oC or 1400oF. The maximum creep rupturing characteristics always are observed in coarser grain cast superalloys that are utilized in the elevated temperature regime. The cracking strengths are a function of time, evidently 1000 h stress potential is smaller than 100 hour potential. The creep potential is a function of extent of creep allowed in an analysis. Following table shows temperature effect on short term mechanical behavior of wrought Nickel Superalloys

Alloys	Form	Ultimate tensile Strength						Yield strength at 0.2% offset at						Tensile extension % at
		21oC or 70oF		540oC or 1000oF		760oC or 1400oF		21oC or 70oF		540oC or 1000oF		760oC or 1400oF		21oC or 70oF		540oC or 1000oF	760oC or 1400oF
		Mpa	ksi	Mpa	ksi	Mpa	ksi	Mpa	ksi	Mpa	ksi	Mpa	ksi	21oC or 70oF		540oC or 1000oF	760oC or 1400oF
Nickel based alloys
Hastelloy C 22	sheet	800	116	625	91	525	76	405	59	275	40	240	35	57	61		63
Hastelloy G30	sheet	690	100	490	71	-	-	315	46	170	25	-	-	64	75		-
Hastelloy S	Bar	845	130	775	112	575	84	455	65	340	49	310	45	49	50		70
Hastelloy X	sheet	785	114	650	94	435	63	360	52	290	42	260	38	43	45		37
Inconel 600	Bar	660	96	560	81	260	38	285	41	220	32	180	26	45	41		70
Inconel 601	Sheet	740	107	725	105	290	42	455	66	350	51	220	32	40	34		78
Inconel 617	Bar	740	107	580	84	440	64	295	43	200	29	180	26	70	68		84
Inconel 617	Sheet	770	112	590	86	470	68	345	50	230	33	230	33	55	62		59
Inconel 625	Bar	965	140	910	132	550	80	490	71	415	60	415	60	50	50		45
Inconel 706	Bar	1310	190	1145	166	725	105	1005	146	910	132	660	96	20	19		32
Inconel 718	Bar	1435	208	1275	185	950	138	1185	172	1065	154	740	107	21	18		25
Inconel 718 aging	Bar	1530	222	1350	196	-	-	1365	198	1180	171	-	-	16	15		-
Inconel 718 Super	Bar	1350	196	1200	174	-	-	1105	160	1020	148	-	-	16	18		-
Inconel X750	bar	1200	174	1050	152	-	-	815	118	725	105	-	-	27	26		-
NImonic 75	bar	745	108	675	98	310	45	285	41	200	29	160	23	40	40		67
Nimonic 80A	bar	1000	145	875	127	600	87	620	90	530	77	505	73	39	37		17
NImonic 90	bar	1235	179	1075	156	655	95	810	117	725	105	540	78	33	28		12
Pyromet 860	bar	1295	188	1255	182	910	132	835	121	840	122	835	121	22	15		18
Rene 41	Bar	1420	206	1400	203	1105	160	1060	154	1020	147	940	136	14	14		11
Rene 95	Bar	1620	235	1550	224	1170	170	1310	190	1255	182	1100	160	15	12		15
Udimet 400	bar	1310	190	1185	172	-	-	930	135	830	120	-	-	30	26		-