Pathways to a family of low-cost, high-performance, metal matrix composites based on aluminum diboride in aluminum.

摘要

The continued development of a new family of metal matrix composites based on the in-situ formation of AlB₂ flakes in liquid aluminum is described. First, a new synthesis technique for the preparation of high aspect ratio AlB₂ is demonstrated. Borax and B₂O ₃ were reacted with molten aluminum to prepare high aspect ratio AlB ₂. The focus then shifts to further understanding the Al-B alloy system. Work on the Al-B alloy system concentrated on the Al_(L) + AlB ₂ $\to$ Al_(L) + AlB₁₂ peritectic transformation and the growth of AlB₂ in aluminum. The equilibrium peritectic transformation temperature was redetermined and found to be 950 ± 5°C. The kinetics of the peritectic transformation were measured and reported for the first time. Cu, Fe, and Si additions were made to the alloy, and their effect on the peritectic reaction was investigated. All three elements shorten the time required for the peritectic reaction to occur. The effect of these three elements on flake growth was also investigated. They each caused a reduction in the size of growing AlB₂ flakes. Finally two samples containing more than 30v% AlB₂ in aluminum were prepared. Their properties were measured. The sample containing 40v% AlB₂ exhibited a flexural strength of 200 MPa. The 35v% sample exhibited a flexural strength of 150 MPa. When the 35v% sample was tested in compression, it exhibited an ultimate strength close to 200 MPa. Its modulus varied from 200–300 GPa depending on the orientation of the loading axis with respect to the flake reinforcement.