Enhanced fatigue crack growth resistance at elevated temperature in TiC/Ti-6Al-4v composite: Microcrack-lnduced crack cl
- PDF / 2,390,229 Bytes
- 8 Pages / 613 x 788.28 pts Page_size
- 46 Downloads / 240 Views
I.
INTRODUCTION
TITANIUM alloys have been used in many applications in which high strength, light weight, and good high-temperature properties are needed. To further improve the specific modulus and strength, strong ceramic phases are added to Ti alloys as reinforcements. In the selection of reinforcing materials, carbide and boride of titanium are excellent choices because of their compatibility with the metal matrix. A notable example of Ti-matrix composites based on a carbide is the composite of TiC and Ti-6A1-4V, produced by mixing TiC particles and Ti-alloy powder via a conventional powder metallurgy procedure, m The resulting composite exhibits improved modulus, strength, and high-temperature stability, u,2,31Although the as-fabricated composite showed extremely low fracture toughness, recent work has shown some promise for improving this: the fracture toughness of the TiC/Ti-6A1-4V composite was increased from 18 to 30 M P a V ~ with an additional thermal annealing treatment, t4.5] The room-temperature fatigue crack growth behavior of as-processed TiC/Ti-6A1-4V composite has been described in Reference 4. The fatigue crack growth properties of the composite are similar to those of Ti-6A1-4V alloy made by powder metallurgy. Although fatigue cracks in the monolithic matrix alloy follow a//3 phase boundaries, they are mixed with cleavage facets of TiC particles in the TiC/Ti-6AI-4V composite. As the fatigue crack propagates through this composite, it chooses no obvious preferred path in the microstructure. This is different from the behavior of fatigue cracks in aluminum alloy-matrix composites, in which cracks tend to avoid reinforcing particles.16-~u Although excellent high-temperature strength has been reported in TiC/Ti composites, little is known of the fatigue properties of these composites at elevated temperatures at which applications of these composites can bring many potential advantagesJ ~,21 In this work, the G. LIU, Graduate Student, D. ZHU, Visiting Researcher, and J.K. SHANG, Assistant Professor, are with the Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Manuscript submitted December 6, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
fatigue crack growth properties of TiC/Ti-6A1-4V composite at an elevated temperature are reported. Contrary to the effect of temperature on fatigue crack growth in most monolithic alloys, fatigue crack growth is retarded when temperature increases from room temperature to 450 ~ This apparently anomalous behavior is unique to the composite and is related to the extensive microcracking of particles at elevated temperatures. The microcracking is shown to induce a high level of fatiguecrack closure, which effectively reduces the crack-growth driving force to slow down fatigue crack growth.
II.
MATERIAL AND P R O C E D U R E
The material used in this study was a 20 vol pct TiC particulate-reinforced Ti-6A1-4V composite made by powder metallurgy. The chemical composition of the matrix alloy is listed
Data Loading...
