Analysis of the creep behavior of silicon carbide whisker reinforced 2124 Al(T4)
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I.
INTRODUCTION
DISCONTINUOUS silicon carbide reinforced aluminum alloy composites have received considerable interest due to several favorable attributes. The presence of the silicon carbide substantially improves the matrix modulus, and results in enhanced matrix strength. 1-7 Further, conventional metal working techniques can be utilized to shape these discontinuously reinforced composites. Finally, low raw material costs coupled with the use of conventional metal working techniques can result in a low cost material. Despite the extensive room temperature 'mechanical property evaluation of the discontinuous reinforced aluminum composites, the elevated temperature behavior of these composites has received relatively little attention. 8'9 In this study, the steady-state creep properties and elevated temperature tensile behavior of silicon carbide whisker reinforced 2124 A1 (SiCw/2124 AI) are reported and discussed. An attempt is made to interpret the observed elevated temperature mechanical behavior of the composite on a mechanistic basis.
II. MATERIAL AND EXPERIMENTAL PROCEDURE The SiCw/2124 AI composite material was supplied by ARCO Chemicals in the form of a 12.7 cm x 1.3 cm extruded plate. The nominal volume fraction of the SiCw was 20 pct. An optical micrograph of the as-received material is presented in Figure 1. The distribution of the SiC within the A1 matrix is fairly homogeneous, although some banding is evident. Also note that in addition to whiskers, some particulate SiC is present. Specimen blanks were cut from the extruded plate parallel to the extrusion axis and were given the following heat treatment prior to machining: solutionizing at 495 ~ in argon for 2 hours, water quench, and natural V.C. NARDONE, Associate Research Scientist, and J.R. STRIFE, SeniorMaterialsScientist,are with UnitedTechnologiesResearchCenter, MS 24, SilverLane, East Hartford, CT 06108. Manuscript submittedMarch 11, 1986. METALLURGICALTRANSACTIONSA
Fig. 1--Optical micrograph of the 20 vol pct SiCw/2124 A1 microstructure. age at room temperature for a minimum of seven days. This is nominally a T4 heat treatment. The T4 heat treatment has no observed effect on the SiCw distribution such that Figure 1 is also indicative of the material in the heat treated condition. Tensile testing of the SiCw/2124 A1 (T4) composite was performed at room temperature, 177 ~ and 288 ~ The stress-strain behavior was determined in an MTS servohydraulic test machine using a constant crosshead deflection rate of 0.127 mm/min. Strain was monitored using a water cooled MTS high temperature axial extensometer and chart recorder. Specimens were held at temperature for 15 minutes prior to testing. Creep testing was conducted in air using a 12,000 lb Model D Satec lever arm creep machine with horizontal self-alignment capabilities. Strain was monitored using an extensometer and dual linear variable differential transformers (LVDT's) with output being monitored by an electric pen strip chart recorder. The extensometer was attached VOLUME18A,JANUARY1987--
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