Evaluation of Adhesion Strength in a Ti/Al 2 O 3 Composite
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EVALUATION OF ADHESION STRENGTH IN A Ti/A1203 COMPOSITE
HSIN-FU WANG*, JOHN C. NELSON*, CHIEN-LI LIN*, WILLIAM W. GERBERICH*, CHARLES J. SKOWRONEK** AND HERVE E. DEVE** *University of Minnesota, Minneapolis, MN 55455. "**MetalMatrix Composites Program, 3M Company, MN 55144.
ABSTRACT The mechanical properties of interfaces in Ti/A120 3 composites were characterized by four point bending and fiber pushout tests. To determine the bi-material fracture as sandwich toughness with four point bending tests, planar interfaces were evaluated 0 0 composites. By changing the processing temperature 0 from 700 C to 1000 C, the interfacial fracture energy was found to increase ug to 950 C. It then decreases when the processing temperature is further increased to 1000 C. This is because of the formation of the intermetallic compound (Ti 3AI). Interfacial shear strength and interfacial frictional stress of 323MPa and 312 MPa were obtained, respectively, by performing pushout tests of the A120 3 fiber reinforced Ti matrix composites. These values are smaller than the shear yielding strength of the Ti matrix which is 525 MPa.
INTRODUCTION Continuous fiber reinforced Ti matrix composites have received attention in the aerospace industry as advanced structural materials because of their high specific strength, excellent corrosion resistance and good high temperature thermal stability[I-3]. The macroscopic mechanical properties of these composites are controlled not only by the mechanical properties of the constituents but also by the adhesion strength of the fiber/matrix interfaces. Usually, bonding and adhesion between the metal and the ceramic are critical to the mechanical properties of the composites. When a metal/ceramic interface in the composite is subjected to excessive external or residual stress, failure will occur along the interface or within one of the two constituents[4][5]. Interfacial debonding and sliding play an important role in determining the overall fracture toughness of the composites under tensile loading. It is recognized that the interfacial debonding and sliding process in the fiber composites are dominated by the interfacial fracture energy and interfacial frictional stress respectively[6]. The main purpose of this paper is to report on the interfacial fracture energy and interfacial frictional stress in Ti/A120 3 composites as measured by four point bending and fiber pushout tests. The relationship between the mechanical properties and microstructure is also discussed.
EXPERIMENTAL PROCEDURE Four point bending tests The test specimen which served as a model system to evaluate the interfacial fracture energy consists of a bimaterial beam with symmetric precracks, as shown in Fig. 1. To make sandwich specimens for the four point bending tests, they were prepared as follows: thin foils of Ti (99.8% pure) and A12 03 plates were immersed in isopropyl alcohol for 10 min and then cleaned in an ultrasonic cleaner for 20 min. They were sandwiched with a 3mm gap between the two foils to form a precrack, wrapped w
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