Synchrotron X-Ray Study of Bulk Lattice Strains in Externally Loaded Cu-Mo Composites

surements can be performed at much reduced exposure times THE load-bearing capacity of a metal matrix composite and in small diffracting volumes, thus allowing for investi(MMC) is dictated by the load transfer occurring from the gating the time dependenceof lattice strains and for mapping compliant, soft matrix to the stiff, hard reinforcements. such strains with a lateral resolution of a fraction of a The load partitioningratio betweenmatrix and reinforcement millimeter. remains constant as long as both components behave in a We have further developed this technique and applied it linear elastic manner. Upon plastic deformation of the mato study lattice strains in copper-molybdenumcomposites. trix, the partitioningratio changes and the reinforcing phases The first goal of the present work is to establish a detailed carry a greater portion of the load. Thus, the composite methodologyfor lattice strain measurements inmechanically becomes mechanically more efficient as a higher portion of loaded samples. As there is only limited experience with the applied load is carried by the reinforcingphase.However, this technique and as the methods to evaluate the raw data with increasing stress in the reinforcement, that phase may are not standardized, the present article examines in detail fracture or debond from the matrix, thus reducing the load the experimental procedures and data evaluation techniques. born by the reinforcement and the overall load-bearing The major sources of experimental error are identified and capacity of the composite, and also often leading to macroappropriatemeasures to minimize these errors are discussed. scopic failure of the composite. The second goal of the present study is to compare, on Experimental measurement of load partitioning between Cu-Mo composites from the same origin, the phase strain the individual phases of MMCs can thus give a wealth of measured by neutron diffraction (as reported by Daymond information on themicromechanicalevolutionof composites et al.) and by synchrotron X-ray diffraction (as reported during deformation. Such measurements have been perin the present paper), thus establishing a direct comparison formed by neutron diffraction in aluminum reinforced with between the two techniques. Finally, the third goal of this various ceramic particles, in NiTi reinforced with TiC article is to use these Cu-Mo composites to further investiparticles, and in a model composite consisting of copper gate howphase strain partitioningduringmechanical loading reinforced withmolybdenumparticulates. Neutron diffracis affected by varying reinforcement volume fraction and tion techniques, however, require long measurement times by matrix plastic deformation reinforcement damage occurand large diffraction volumes because of the small neutron ring at large macroscopic plastic strains. flux available at existing thermal neutron sources and the