ADVANCED S UR F AC E E N G I N E E R I N G BY A P P L I C A T I O N OF H I P TECHNOLOGY
H I P ULTRASONICS: AN IN-SITU METHOD FOR DENSIFICATION MONITORING
L.E. Tidbury, (H.I.P. Ltd, Sheepbridge, UK). The paper describes the use of HIP to engineer the surface properties of metal parts. HIP is effecive in the promotion of diffusion controlled reactions and this can be carried out by means of additions to the process gas or by means of solid materials applied to the surface of the parts to be t re a te d prior to HIPing. Carbon and nitrogen have been added in this way. The modified surface layers have been characterized and the changes are related to the HIP cycle parameters.
M. Ganor, et al, (NRCN, Beer-Sheva, Israel). The paper describes the use of sensors placed inside the HIP vessel to monitor dimensional changes in canned materials. The measurements made were related to changes in the density of the encapsulated materials. Attention was drawn to the need for f u r t h e r s t u d i e s of d e n s i f i c a t i o n mechanisms and their dependence on process parameters in order to establish the validity of HIP diagrams.
DIRECT DIGITAL C O N T R O L F O R ISO STA TI C P R ES S ES W. Vandijck, A. Minnebo, (Viteck NV, SintNiklass, Belgium). Attention is drawn to the importance of process control in HIPing and to the need for f u r t h e r d e v e l o p m e n t s in c o n t r o l procedures and instrumentation. A new c o m p u t e r a p p r o a c h to t e m p e r a t u r e measurement and control was described. I m p r o v e m e n t s on e x i s t i n g a u t o m a t i c c o n t r o l an d m a n u a l c o n t r o l by an experienced operator were reported. The computer program uses a model of the HIP characteristics and looks ahead at the temperature and pressure profile which has been set. Use is made of a standard personal computer which, controls process parameters directly. C O N T R O L OF T H E E N V I R O N M E N T W I T H I N A H O T I S OS T A T I C PRESS Crum, (National Forge Co, Andover, MA, USA). The control of pressure and temperature within HIPing is discussed. Data concerning the deviation of A from the ideal gas laws are presented with a mathematical model of a temperature control system with the resulting transient behaviour. Predictions are compared with observed results. D I L A T O M E T R I C STUDY OF D E N S I F I C A T I O N KINETICS OF S O M E POWDER MATERIALS UNDER HIP CONDITIONS M. Dietze, et al, (Institfit ffir Angewandte Werkstofforschung, Forschungszentrum Julich GmbH, Julich, Germany). The p ap er described the use of a dilatometer to study the time dependent densification of powder materials. The data obtained is of value both in understanding the mechanisms of densification and in designing and controlling HIP cycles. A number of ceramic and metal powder systems was studied. Time/densification curves are presented.
D E V E L O P M E N T AND A P P L I C A T I O N S OF A D I L A T O M E T E R FOR O P T I M I Z A T I O N OF SINTER, P O S T H I P AND S I N T E R / H I P CYCLES A. Kuhne, et al, (University of Karlsruhe, Karlsruhe, Germany). The development of a dilatometer for use in HIP systems at temperatures up to 2200°C and pressures up to 200 MPa was d e s c r i b e d . The d e t e c t i o n of p h a s e transformations by differential thermal analysis (DTA) is also described. Results from the two techniques were in agreement. The dilatometer permits the detection of dimensional changes over the complete range of HIPing and the results can be collected, corrected and manipulated by a computer which is also used for process control. Density and shrinkage kinetics, as a function of temperature and heating rate, and pressure and rate of pressurization, can be determined at any instant and the instant of pressurization optimized. N U M E R I C A L S I M U L A T I O N OF I S O S T A T I C P R E S S I N G P R O C E S S FO R T H E E L I M I N A T I O N OF DEFECTS IN M E T A L L I C AND CERA MI C PARTS G.N. Pande, J. Middleton, (University College, Swansea, UK). Defects arising in the compaction of powders by CIP and HIP were discussed with respect to causes and the measure taken for their correction. Attention was drawn to the need for a more fundamental and rigorous approach to the quantification of defects. M I C R O M E C H A N I C S OF D E N S I F I C ATI O N AND D I S T O R T I O N I~B. Clough, RJ. Schaefer, (National Institutute of Standards and Technology, Galthersburg, MD, USA). Whilst compaction under purely isostatic pressure is free from distortion the introduction of any shear stresses, for example by the canister, may cause a change in the shape of a powder compact. The paper describes a plasticity theory for both s h a p e and v o l u m e ch an g es in compacts. It may be applied to both
p o r o u s a n d p a r t i c u l a t e m e d i a . By combination with the Ashby m i c r o m e c h a n i c a l m o d e l for p o w d e r compaction, modified to allow for work hardening and applied to particulate c o m p a c t s it a g r e e s f a v o u r a b l y w i t h experimental data from a range of powder compacts in uniaxial and isostatic stress states using data from Cu powders in Cu containers. Finite element modelling may be applied. N U M E R I C A L M O D E L L I N G OF HIP: I N FLU EN CE OF O P E R A T I N G P A R A M E T E R S AND R H E O L O G Y OF TH E P O R O U S M A T E R I A L C. Dellis, et al, (Institut Mecanique de Grenoble, Grenoble, France). Finite element ~ethods have been used to construct a model of the HIP process. Thermal, elastic and viscoplastic effects as well as the porosity of the material have been taken into account. Process parameters are used in the model. The influence of the various parameters on deformation predicted by the model for two industrial superalloy components, a long tube and a ring of more complex shape, have been examined with regard to the HIP cycle, the thermal dit~sivity of the materials and how this varies with porosity, characteristics of the container and the rheological properties of the powder.
USE OF PRESSURE SINTER OR HIP FOR CEMENTED CARBIDES B. North, et al, (Kennametal Inc., Latrobe, PA, USA). The paper considers the interaction of p r o c e s s v a r i a b l e s a n d c h a n g e s in composition and m i c r o s t r u c t u r e with changes in physical and m e c h a n i c a l properties of cemented carbides subjected to HIP. The relevance of post-densification treatments, such as grinding or coating, are discussed in terms of how surface condition may override or reinforce internal changes in microstructure due to pressure sinter of HIP. Conclusions are drawn linking the use of pressure sinter or HIP to carbide grade, process route, surface condition and product application.
SHRINKAGE STUDIES ON C E M E N T E D CARBIDES DURING GAS P R E S S U R E SINTERING B.O. Haglund, (AB Sandvik Coromant, Stockholm, Sweden). Dilatometry has been used to study the kinetics of sintering of cemented carbides at pressures up to 20 MPa in A or N2. The resolution of the dilatometer was 1 p_m which was sufficiently sensitive to follow changes during sintering as well as the solidification of the binder phase.
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