2003 PhD University of Southampton
1999 BEng University of Leicester
Casting & Solidification
Despite the widespread use of single-crystal nickel-base superalloys, there were fundamental questions related to the solidification of these alloys which remain unanswered.
In the directional solidification casting process to produce single-crystal components, primary solidification commences with the formation of γ dendrites. This is followed by the formation of non-equilibrium inter-dendritic constituent up to the terminal stages of solidification. Recent work has shown that the inter-dendritic constituents consists of two distinct morphologies (i) fine γ / γ' morphology, and (ii) coarse cellular γ' separated by narrow γ channels.
Solution Heat Treatment
To meet increasingly demanding service conditions, higher contents of dense refractory elements were added to single-crystal nickel-base superalloys. Associated with these additions however were the formation of severely segregated as-cast microstructures which requires homogenisation via solution heat treatment prior to service.
Solution heat treatment processes need to be optimised to produce homogenised materials without incipient melting and within acceptable cost and time constraints in industry.
Phase Stability of Superalloys
The higher contents of dense refractory elements in newer generations of alloys also have the tendency to increase the susceptibility of these alloys to the formation of topologically-closed-packed (TCP) phases after prolonged exposure at elevated temperatures. These TCP phases are detrimental to the alloys as they are brittle and may therefore act as crack initiation sites. In addition, the formation of these TCP phases depletes the microstructure of refractory elements critical for high temperature performance.
Care is required during alloy design to balance the alloy compositions in order to achieve the required properties against the phase stability of these alloys.
Materials Testing – Differential Scanning Calorimetry, Thermogravimetric Analysis, etc.
Small-scale Mechanical Testing – Electro-Thermo Mechanical Testing
Trace element analyses - Laser Ablation-Inductive Coupled Plasma-Mass Spectrometry
Environmental Protection Performance
H.T. Pang, N. D'Souza, H.B. Dong, H.J. Stone, C.M.F. Rae "Detailed Analysis of the Solution Heat Treatment of a Third-Generation Single-Crystal Nickel-Based Superalloy CMSX-10K" Metallurgical and Materials Transactions A, 47A (2016), 889-906.
H.T. Pang, I.M. Edmonds, C.N. Jones, H.J. Stone, C.M.F. Rae "Effects Of Y And La Additions On The Processing And Properties Of a Second Generation Single Crystal Nickel-Base Superalloy CMSX-4" Superalloys 2012, E.S. Huron, R.C. Reed, M.C. Hardy, M.J. Mills, R.E. Montero, P.D. Portella and J. Telesman (Eds), TMS 2012, 301-310.
H.T. Pang, L. Zhang, R.A. Hobbs, H.J. Stone, C.M.F Rae "Solution Heat Treatment Optimization Of Fourth-Generation Single-Crystal Nickel-Base Superalloys" Metallurgical and Materials Transactions A, 43A (2012), 3264-3282.
H.T. Pang, R.A. Hobbs, H.J. Stone, C.M.F. Rae "A Study of the Effects of Alloying Additions on TCP Phase Formation in 4th Generation Nickel-Base Single-Crystal Superalloys" Advanced Materials Research, 278 (2011), 54-59.
H.T. Pang, H.B. Dong, R. Beanland, H.J. Stone, C.M.F. Rae, P.A. Midgley, G. Brewster, and N. D’Souza "Microstructure and Solidification Sequence of the Interdendritic Region in a Third Generation Single-Crystal Nickel-Base Superalloy" Metallurgical and Materials Transactions A, 40A (2009), 1660-1669.
H.T. Pang, P.A.S. Reed "Microstructure Effects on High Temperature Fatigue Crack Initiation and Short Crack Growth in Turbine Disc Nickel-base Superalloy Udimet 720Li" Materials Science and Engineering A, 448 (2007), 67–79.
H.T. Pang, P.A.S. Reed "Fatigue Crack Initiation and Short Crack Growth in Nickel-base Turbine Disc Alloys — the Effects of Microstructure and Operating Parameters" International Journal of Fatigue, 25 (2003), 1089–1099.
H.T. Pang, F. Li, S. Pahlavanyali, I.M. Edmonds, G. Brewster, C.M.F. Rae "Effects of Sea Salt on the Oxidation of CMSX-4® at 1100 °C" Superalloys 2016, M.C. Hardy, E.S. Huron, U Glatzel, B. Griffin,B. Lewis, C. Rae, V. Seetharaman, S. Tin (Eds), TMS 2016, 949-958.
H.T. Pang, M.C. Hardy, N. Hide, I.M. Wilcock, M.B. Henderson, P.A.S. Reed "Comparison of Fatigue Crack Propagation in Nickel-Base Superalloys RR1000 and Udimet 720Li" Materials Science and Technology, 32 (2016), 22-39.
S. Pahlavanyali, H.T. Pang, F. Li, S. Bagnall and C.M.F. Rae "On the effect of salt deposits on the oxidation behaviour of CMSX-4 above 1000 °C" Materials Science and Technology, 30 (2014), 1890–1898.
A. Bhowmik, H.T. Pang, I.M. Edmonds, C.M.F. Rae, H.J. Stone "Effect of Silicon Additions on the High Temperature Oxidation Behaviour of Cr-Cr2Ta Alloys" Intermetallics, 32 (2013), 373-383.
A. Bhowmik, H.T. Pang, S. Neumeier, H.J. Stone, I. Edmonds "Microstructure and Oxidation Resistance of Cr-Ta-Si Alloys" Materials Research Society Symposium Proceedings, 1295 (2011), 323-328.
H.T. Pang, P.A.S. Reed "Microstructure Variation Effects on Room Temperature Fatigue Threshold and Crack Propagation in Udimet 720Li Ni-base Superalloy" Fatigue Fract Engng Mater Struct 32 (2009), 685–701.
H.T. Pang, P.A.S. Reed "Effects of Microstructure on Room Temperature Fatigue Crack Initiation and Short Crack Propagation in Udimet 720Li Ni-base Superalloy" International Journal of Fatigue, 30 (2008) 2009–2020.
S. Everitt, M.J. Starink, H.T. Pang, I.M. Wilcock, M.B. Henderson and P.A.S. Reed "A Comparison of High Temperature Fatigue Crack Propagation in Various Subsolvus Heat Treated Turbine Disc Alloys" Materials Science and Technology, 23 (2007), 1419-1423.