Effect of Hot Isostatic Pressing Loading Route on Microstructure and Mechanical Properties of Powder Metallurgy Ti2AlNb Alloys

Abstract

Abstract:

In this work, hot isostatic pressing (HIPing) technique was used to densify the Ti₂AlNb pre-alloyed powder. The influence of HIPing loading route parameters (temperature and rates of heating and pressurizing) on microstructure and properties of PM Ti₂AlNb alloys was studied. The results showed that HIPing loading route parameters affected the densification process and mechanical properties (especially high temperature rupture lifetime) of PM Ti₂AlNb alloys in the present work. A finite element method (FEM) model for predicting the final densification was developed and was used to optimize the HIPing procedure.

Key words: Ti-22Al-24Nb-0.5Mo alloy, Hot isostatic pressing, Porosity, Non-uniform densification, Rupture lifetime

Wu Jie,Guo Ruipeng,Xu Lei,Lu Zhengguan,Cui Yuyou,Yang Rui. Effect of Hot Isostatic Pressing Loading Route on Microstructure and Mechanical Properties of Powder Metallurgy Ti2AlNb Alloys[J]. J. Mater. Sci. Technol., 2017, 33(2): 172-178.

Figures/Tables 11

Fig.1 Mild steel capsules of (a) d?=?40?mm, h?=?140?mm; (b) d?=?160?mm, h?=?140?mm

Fig.2 Thermal physical parameters of as-HIPed Ti2AlNb alloys as function of temperature: (a) elastic modulus and Poisson ratio; (b) heat capacity; (c) thermal conductivity; (d) average coefficient of linear expansion

Table 1 Chemical compositions of Ti2AlNb pre-alloyed powder and as-HIPed compacts (wt%)

Samples	Ti	Al	Nb	Mo	O	N	H	Ar
Pre-alloyed powder	Bal.	10.5	41.0	0.88	0.069	0.0080	0.0050	<0.0005
As-HIPed compacts	Bal.	10.3	41.4	0.90	0.065	0.0100	0.0010	<0.0005

Fig.3 Characterization of atomized powder: (a) typical morphology of the atomized Ti2AlNb powders; (b) accumulative mass distribution of the atomized Ti2AlNb powders; (c) DSC thermogram of Ti2AlNb pre-alloyed powder heating from 150 to 1200?°C[3]

Fig.4 Microstructure of PM Ti2AlNb alloy after HIPing at: (a) 920?°C/130?MPa/3?h; (b) 980?°C/140?MPa/3?h; (c) 1030?°C/140?MPa/3?h; (d) phase distribution observed by EBSD analysis of the sample HIPed at1030?°C/140?MPa/3?h (yellow color shows α2 phase, red color shows B2 phase, and blue color shows O phase)

Fig.5 (a) Microstructure of PM Ti2AlNb alloy after HIPing at 920?°C/130?MPa/3?h, (b) EPMA mapping of Al element showing micro-segregation along the PPBs in Ti2AlNb powder compacts, (c) EPMA mapping of Nb element showing micro-segregation along the PPBs in Ti2AlNb powder compacts

Table 2 Comparison of mechanical properties for PM Ti2AlNb alloys HIPed at different temperatures

HIPing conditions	T (°C)	0.2% YS (MPa)	UTS (MPa)	EI. (%)	L (h)
920?°C/130?MPa/3?h	20	923	1024	7	28
920?°C/130?MPa/3?h	650	565	708	16	28
980?°C/140?MPa/3?h	20	891	1023	7	36
980?°C/140?MPa/3?h	650	590	723	16	36
1010?°C/140?MPa/3?h	20	850	1030	9	-
1010?°C/140?MPa/3?h	650	599	742	16	-
1030?°C/140?MPa/3?h	20	862	1065	11	49
1030?°C/140?MPa/3?h	650	603	752	14	49

Fig.6 Stress-strain curves of (a) Ti-6Al-4V and (b) Ti2AlNb powder compacts at different temperature at έ?=?0.001?s-1

Fig.7 Temperature and pressure profile of HIPing Route 1 and HIPing Route 2

Table 3 Comparison of mechanical properties for heat-treated PM Ti2AlNb alloys from different HIPing routes

Conditions	T (°C)	0.2% YS (MPa)	UTS (MPa)	EI (%)	L (h)
HIPing Route 1?+?HT	20	834	995	10	93
HIPing Route 1?+?HT	650	568	760	10	93
HIPing Route 2?+?HT	20	905	1032	11	75
HIPing Route 2?+?HT	650	695	783	17	75

Fig.8 Relative density distribution of powder compacts after (a) HIPing Route 1 and (b) HIPing Route 2

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