Eric Klier

Mechanical Properties of Steel Encapsulated Metal Matrix Composites

This research evaluates a coefficient of thermal expansion (CTE) mismatch induced residual compressive stress approach as a means of improving the ductility of metal matrix composites (MMCs). MMCs are frequently incorporated into advanced material systems due to their tailorable material properties. However, they often have insufficient strength and ductility for many structural applications. By combining MMCs with high strength steels in a hybridized, macro composite materials system that exploits the CTE mismatch, materials systems with improved strength, damage tolerance, and structural efficiency can be obtained. Macro hybridized systems consisting of steel encapsulated light metal MMCs were produced with the goal of creating a system which takes advantage of the high strength, modulus, and damage tolerance of steels and high specific stiffness and low density of MMCs while mitigating the high density of steels and the poor ductility of MMCs. Aluminum and magnesium based particulate reinforced MMCs combine many of the desirable characteristic of metals and ceramics, particularly the unique ability to tailor their CTE. This work aims to compare the performance of macro hybridized material systems consisting of aluminum or magnesium MMCs reinforced with Al2O3, SiC, or B4C particles and encapsulated by A36 steel, 304 stainless steel, or cold worked Nitronic® 50 stainless steels.

Evaluation of Intermetallic Reaction Layer Formation Within Steel Encapsulated Metal Matrix Composites

Macro hybridized systems consisting of steel encapsulated light metal matrix composites (MMCs) deliver a low cost/light weight composite with enhanced mechanical properties. By exploiting the high strength, modulus, and damage tolerance of steels and the high stiffness and low density of MMCs the resultant macro hybridized systems alleviates the high density of steel and the poor ductility of MMCs. The resultant system, when properly designed, offers higher specific properties and a more structurally efficient system can be attained. However, the combination of these dissimilar materials, specifically iron and aluminum, often results in the formation of intermetallic compounds. In certain loading situations, these typically brittle intermetallic layers can result in degraded performance. In this research, X-ray Diffraction (XRD), X-ray Energy Dispersive Spectroscopy (EDS), and Electron Backscatter Diffraction (EBSD) are utilized to characterize the intermetallic reaction layer formed between an aluminum or magnesium MMCs reinforced with Al2O3, SiC, or B4C particles and encapsulated by A36 steel, 304 stainless steel, or Nitronic® 50 stainless steel.