Microstructure and yield strength of ultrafine grained aluminum processed by hot isostatic pressing

The correlation between the microstructure and the yield strength of a specimen produced by hot isostatic pressing (HIP) of commercial purity aluminum nano-powder was studied. It was found that the bulk sample can be regarded as a composite containing microcrystalline grains embedded in an ultrafine grained matrix. The composite-like microstructure results in a bimodal hardness distribution as shown by nanoindentation. The yield strength values for both the ufg matrix and the mc grains were calculated from the characteristic parameters of the microstructure. The yield strength of the composite estimated by using a simple rule of mixture was in good agreement with the value determined by compression test. It was revealed that the majority of the strengthening can be attributed to the dislocations in the ufg matrix and the alumina dispersoids formed during HIP process.