The hot isostatic processing characteristics of 70/30 cupronickel castings. KING, S. Available from Sheffield Hallam University Research Archive (SHURA) at: http://shura.shu.ac.uk/19916/ This document is the author deposited version. You are advised to consult the publisher's version if you wish to cite from it. Published version KING, S. (1992). The hot isostatic processing characteristics of 70/30 cupronickel castings. Doctoral, Sheffield Hallam University (United Kingdom).. Copyright and re-use policy See http://shura.shu.ac.uk/information.html Sheffield Hallam University Research Archive http://shura.shu.ac.uk Sheffield City Polytechnic Library REFERENCE ONLY ProQuest Number: 10697222 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10697222 Published by ProQuest LLC(2017). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 THE HOT ISOSTATIC PROCESSING CHARACTERISTICS OF 7030 CUPRONICKEL CASTINGS S. King A thesis submitted in partial fulfilment of the requirements of Sheffield Hallam University for the degree of Doctor of Philosophy School of Engineering 1992 '• P O ! . H uv Tri u;( (06^133 t\ <4> PREFACE The work reported in this thesis was carried out at the School of Engineering, Sheffield City Polytechnic between October 1988 and December 1991 whilst the candidate was registered for a higher degree. The candidate has not during the above period of registration for the CNAA degree of Ph.D. been registered for any other CNAA award or for any university degree. The results presented here are, as far as can be certain, original except where reference has been made to previous work. A post graduate course was attended at Sheffield City Polytechnic during the above period in the following subjects: Computer Programming / Numerical Analysis and Economics. In addition short courses on Scanning Electron Microscopy Techniques and Thermal Stress Analysis were also attended, both held at Sheffield City Polytechnic. The author has attended a conference on Isostatic Pressing "IS04" held at Stratford upon Avon, 5-7 November 1990, and presented a paper entitled "The Hot Isostatic Processing Characteristics Of 70/30 Cupronickel Castings", the paper is shown in Appendix 1. The author also published a review paper entitled "The Effect Of HIP On Cast Cupronickel Alloys" in the Trades Foundry Journal, 24 February 1989, as shown in Appendix 2. As a result of this research programme and its findings an addition has been made to the Naval Engineering Standard NES 824 concerning the optimum processing parameters for the recovery of cupronickel castings. The relevant part of the Engineering Standard is shown in Appendix 3. S . King January 1992. ACKNOWLEDGMENTS The author would like to express her appreciation to Vickers Ship-Building and Engineering Limited for supplying cast NES 824 material, and to the Ministry of Defence Bath, for carrying out quantitative corrosion tests on both cast and hot isostatically processed 70/30 cupronickel. Grateful appreciation is also made to H.I.P Limited for use of their laboratory HIP facilities as well as to Dr. B.A. Rickinson (industrial supervisor) and Dr. L.E. Tidbury for numerous helpful discussions and constant encouragement. Many thanks to the technicians, administrative staff and lecturing staff of the Department of Metals and Materials Process Engineering for their help and support. Thanks also to Professor D. Tidmarsh for his support. Grateful thanks are sincerely expressed to Dr. A.J. Fletcher for his interest, guidance and constant encouragement and support throughout the course of this work. Thanks are also expressed to Dr. H. Atkinson (second supervisor) School of Materials, Sheffield University, for numerous helpful discussions. Finally I would like to pay tribute to my parents, Peter and friends for their patience, support and constant encouragement. 3 THE HOT ISOSTATIC PROCESSING CHARACTERISTICS OF 70/30 CUPRONICKEL CASTINGS by Susan King SYNOPSIS 70/30 cupronickel designated in the Naval Engineering Standard NES 824 is associated with high integrity cast components. However this specification restricts the use of welding to recover castings if they are to be wetted by sea water. Hot isostatic pressing is considered to be an alternative recovery process. The mechanisms of pore closure and the processing parameters for successful recovery have been investigated together with their effect on microstructural and mechanical property characteristics. In addition models have been identified which accurately predict pore closure rates in cupronickel castings. Hot isostatic pressing trials were carried out using processing temperatures within the range 850°C and 1025°C and argon gas pressures of 45MPa to 145MPa. Two time, temperature, pressure procedures were investigated; successive cycles of short duration and single continuous cycles. The investigations were carried out on 70/30 cupronickel (NES 824) specimens that contained artificially introduced porosity in the form of closed internal pores and surface-connected porosity: the latter required encapsulation prior to processing. These investigations have revealed that for the removal of surface-connected porosity, successive cycles of short duration were more effective in closing large pores than a single cycle of the same total duration. In addition elongated pores of small diameter were removed more quickly than pores of equivalent volume porosity but smaller aspect ratio. Shorter recovery times were required for the consolidation of internal porosity in comparison with surface-connected porosity indicating that encapsulation restricts the densification process. Initially the rate of densification during HIPping was rapid suggesting that plastic flow was occurring. Subsequent densification probably by viscous flow mechanisms occurred at a much lower rate once the sustain conditions had been reached. This fall off in the densification rate applied in particular to encapsulated castings. The optimum processing conditions for the successful densification of 70/30 cupronickel castings are short sustain times of 45 minutes, a temperature of 950°C and argon gas pressures within the range 83-103MPa. Hot isostatic processing significantly increases the ductility of 70/30 cupronickel castings without a reduction in strength and has no adverse effects on corrosion resistance. NOMENCLATURE A,B Parameters used in the Standard Linear Solid equation; a Average contact area at neck (m2)^. C Constant; p Relative density (kg/m3); D Packing density; Do Initial relative density; Dyield Relative density from plastic yielding; Dc Critical density at which pores close; D* Densification rate (/s); Deff Effective diffusion coefficient; Dl Lattice diffusion coefficient; Dgb Grain boundary diffusion coefficient; £Db Boundary diffusion coefficient times boundary thickness (m3/s) ; Dv Volume diffusion coefficient (m2/s); E Youngs Modulus (GPa); G Grain diameter (m); G Shear modulus (MPa); k Boltzmann's constant (J/k); n Number of pores in unit volume of material; P External pressure (MPa); Peff Effective pressure on a neck (MPa); P0 Out-gassing pressure (MPa); P0 Equivalent pressure caused by surface tension (MPa); P. Gas pressure inside a closed pore (MPa); R Particle radius (m); R' Radius of unit sphere containing one particle (m) ; 5 T Absolute temperature (K); t Time (s); V Volume (m3) ; X Neck radius (m); Z Number of contacts per particle; y Surface energy (J/m2) ; e0,(J0,n Creep parameters (s'1,MPa) ; n Atomic or molecular volume (m3) ; oy Yield stress (MPa); Q Activation energy (kJ/mol); R Gas constant (J/mol.K); D Poissons1 ratio; r^ Viscosity (GPa.s); ^ Coefficient of viscosity; rc Critical yield stress (MPa); n,e Material constants; e creep Creep strain; creep Rate of creepc strain;' €p Plastic strain; ejj Strain tensor; Sjj Stress tensor; <p Material constant used in the Standard Linear Solid equation (s'1) ; o Stress (MPa); a0 Hydrostatic stress (MPa); 8° Hydrostatic strain; a xx ) ciyy ) Stress in x,y and z directions; CTyy > 6 E XX ) Strain in x,y and z directions. eyy > ezz ) YIELD Compaction by plastic yielding when the pressure is applied. V-DIFF1S Surface-tension driven densification by volume from neck boundary, Stage 1. B-DIFF1S Surface-tension driven densification by boundary diffusion from neck boundary, Stage 1. V-DIFF2S Surface-tension driven densification by volume diffusion from neck boundary, Stage 2. B-DIFF2S Surface-tension driven densification by boundary diffusion from neck boundary, Stage 2. V-DIFF1 Pressure-driven densification by volume diffusion from neck boundary, Stage 1. B-DIFF1 Pressure-driven densification by boundary diffusion from neck boundary, Stage 1. V-DIFF2 Pressure-driven densification by volume diffusion from neck boundary, Stage 2. B-DIFF2 Pressure-driven densification by boundary diffusion from neck boundary, Stage 2, PL-CRP1 Pressure-driven densification by power-law creep, Stage 1. PL-CRP2 Pressure-driven densification by power-law creep, Stage 2. NH-CRP1 Pressure-driven densification by volume and boundary