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Precipitation Strengthened High Strength, High Conductivity Cu-Cr-Nb Alloys Produced by Chill Block Melt Spinning

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Precipitation Strengthened High Strength, High Conductivity Cu-Cr-Nb Alloys Produced by Chill Block Melt Spinning NASA Contractor Report 185144 _" / i Precipitation Strengthened High Strength, High Conductivity Cu-Cr-Nb Alloys Produced by Chill Block Melt Spinning David L. Ellis and Gary M. Michal Case Western Reserve University Cleveland, Ohio September 1989 Prepared for Lewis Research Center Under Grant NGT-50087 v National Aeronautics and Space Administration (NA_A-CP-I,3_,I4_) p_Lr IPITATIq'_,. bTi<' Nc, i *_N_: :_ 9 t]- L 1 d _ _) HTL_ "_[R[iNIbTt;, !'tl._,i': (_,q,t'_'i_'-|V,,, I TV, r: . rtj-_.r-_',!i). ALLnYR: oK.......,.,YLFU .Y £iIILL qL_)L! K '"_ t. l :; _ [ N,_I_w._" _ Fin-_l K_Hor_- _tl. ]. Tll}.iJ (L:)s :_ wJqLnrr_ t x- PRECIPITATION STRENGTHENED HIGH STRENGTH, HIGH CONDUCTMTY CU-CR-NB ALLOYS PRODUCED -. BY CHILL BLOCK MELT SPINNING ABSTRACT by DAVID LESLIE ELLIS There are many potential applications for materials that possess a combination of high strength, high conductivity, and good long term stability at elevated temperatures. In an effort to achieve this combination of properties a series of Cu-based alloys containing 2 to 10 a/o Cr and 1 to 5 a/o Nb were produced by chill block melt spinning (CBMS). The melt spun ribbons were consolidated and hot rolled to sheet for testing. The desire was to produce a supersaturated Cu-Cr-Nb solid solution from which the high melting point intermetallic compound Cr2Nb could be preferentially precipitated to precipitation strengthen the Cu matrix. By using the intermetallic phase, it was hoped that the precipitates would not coarsen readily and lose their strength as with Cu-Cr alloys do when exposed to elevated temperatures, particularly above 500 ° C. The results show that the materials possess electrical conductivities in excess of 90% that of pure Cu at 200 ° C and above. This implies that the thermal conductivities of these alloys are near that of pure Cu at temperatures above 200 ° C. The strengths of the Cu-Cr-Nb alloys were much greater than Cu, Cu-0.6 Cr, NARloy-A, and NARloy-Z in the as-melt spun condition. The strengths of the consolidated materials were less than Cu-Cr and Cu-Cr-Zr below 500 ° C and 600 ° C respectively, but were significantly better above these temperatures. The strengths of the consolidated materials were greater than conventional wrought NARloy-Z, the material currently used in rocket nozzles, at all temperatures. GLIDCOP possessed similar strength levels up to 750°C when the strength of the Cu-Cr-Nb alloys begins to degrade. The long term stability of the Cu-Cr-Nb alloys was measured by the microhardness of aged samples and the growth of precipitates. The microhardness measurements indicate that the alloys overage rapidly, but do not suffer much loss in strength between 10 and 100 hours which confirms the results of the electrical resistivity measurements taken during the aging of the alloys at 500 ° C. The loss in strength from peak strength levels is significant, but the strength remains exceptionally good. TEM of the as-melt spun samples revealed that the Cr2Nb precipitates formed in the liquid Cu during the chill block melt spinning, indicating avery strong driving force for the formation of the precipitates. TEM of the aged and consolidated materials indicates that the precipitates do coarsen considerably, but remain in the submicron size range. ii ACKNOWLEDGEMENTS I would like to thank NASA Lewis Research Center for supporting my work through the NASA Graduate Student Fellowship Program. I would like to extend special thanks to Hugh Gray, Norman Orth, John King, Ivan Locci, Mohan Hebsur, Gordon Watson, James Knight, John Juhaus, David Hull, Todd Leonhardt, Robert Dreshfield, Ralph Garlick, David Plumer, Chuck Boros, Adrienne Veverka. Peg_ Yancer, and Ted Bloom. I would also like to thank Professors Mark DeGuire, John Lewandowski, and Robert Savinell for kindly consenting to sit on my committee. And finally a special thanks to my advisor Gary Michal for all of his help. iii Table of Contents Abstract ................................................................................................................ i Acknowledgements ............................................................................................. iii 1 Introduction ..................................................................................................... 1 1.1 Outline of Problem ................................................................................. 1 1.2 Purpose of Study ..................................................................................... 3 1.3 Alloy Selection ......................................................................................... 3 2 Literature Review ............................................................................................ 6 2.1 Phase Diagrams ....................................................................................... 6 2.1.1 Cu-Cr Phase Diagram ..................................................................... 6 2.1.2 Cu-Nb Phase Diagram .................................................................... 8 2,1.3 Cr-Nb Phase Diagram .................................................................... 10 2.1,4 Cu-Cr2Nb Pseudo-Binary Phase Diagram ................................... 12 2.2 Precipitation and Dispersion Strengthening ....................................... 13 2.2.1 Effective Particle Spacing .............................................................. 16 2.2.2 Obstacle Strengths ......................................................................... 19 2.2.2.1 Chemical Strengthening ....................................................... 19 2.2.2.2 Stacking Fault Energy Strengthening ................................ 21 2.2.2.3 Modulus Strengthening ......................................................... 22 2.2.2.4 Order Strengthening ............................................................. 22 2.2.2.5 Coherency Strengthening ..................................................... 24 2.2.2.6 Orowan Strengthening .......................................................... 28 iv 2.2.2.7 Ashby-Orowan Model ............................................................. 30 2.2.3 Multiple Precipitate Phases .......................................................... 32 2.3 Nucleation and Growth of Precipitates ................................................ 35 2.3.1 Nucleation of Precipitates ............................................................. 36 2.3.2 Growth of Precipitates ................................................................... 36 2.3.3 Coarsening of Precipitates ............................................................. 37 2.4 Mechanical Properties of Cu-Based Alloys .......................................... 39 2.4.1 Precipitation Strengthened Cu-Based Alloys ............................. 43 2.4.1.1 Cu-Cr Alloys ............................................................................ 44 2.4.2 Dispersion Strengthened Cu-Based Alloys ................................. 47 2.4.3 Cu-Nb In Situ Composites ............................................................. 48 2.5 Rapid Solidification Technology ............................................................ 49 2.5.1 Rapid Solidification Techniques ................................................... 49 2.5.2 Chill Block Melt Spinning ............................................................. 53 2.5.3 Advantages of RST Processing ...................................................... 56 2.5.4 Consolidation Techniques ............................................................. 58 2.6 Electrical Resistivity and Thermal Conductivity ................................ 59 2.6.1 Wiedmann-Franz Law .................................................................... 60 2.6.2 Experiment_. Measurement of Electrical Resistivity and Thermal Conductivity .................................................................... 63 2.6.3 Effect of Solute Atoms on Electrical Resistivity and Thermal Conductivity .................................................................................... 65 2.6.4 Effect of Temperature on Electrical Resistivity ......................... 71 2.6.5 Reversion Phenomena in Cu-Cr, Cu-Zr, and Cu-Cr-Zr Alloys 73 2.6.6 Electrical Resistivity and Thermal Conductivity of Various Materials .......................................................................................... 77 3 Experimental Procedure ................................................................................ 80 V 3.1 Master Alloy Melting .............................................................................. 80 3.2 Differential Thermal Analysis (DTA) ................................................... 82 3.3 Chill Block Melt Spinning ...................................................................... 83 3.4 Aging Study .............................................................................................. 84 3.5 Consolidation of Cu-Cr-Nb Alloys ......................................................... 85 3.6 X-ray Diffraction ...................................................................................... 89 3.7 Optical Microscopy .................................................................................. 89 3.8 Transmission Electron Microscopy (TEM) .......................................... 91 3.9 Microhardness Measurements .............................................................. 92 3.10 Tensile Testing ...................................................................................... 92 3.11 Electrical Resistivity Measurements .................................................
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