Effects of Changes in Test Temperature on Tensile Properties and Notched Vs Fatigue Precracked Toughness of a Zr-Based B
- PDF / 3,870,369 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 59 Downloads / 212 Views
DUCTION
BULK metallic glass (BMG) alloys have promising properties such as high strength, formability, and good surface finish.[1–3] However, they are also prone to catastrophic failure via shear localization at temperatures well below their glass transition temperature (Tg),[4–6] which typically results in zero tensile ductility. To address this, a variety of in situ BMG matrix composites (BMGMCs)[7–9] have been developed to improve tensile ductility at room temperature. An in situ BMGMC consists of an amorphous matrix and a crystalline second phase that has been precipitated directly from the melt.[7] The composite microstructure promotes ductility at room temperature by two mechanisms that encourage the formation of numerous shear bands that are unable to propagate to failure. First, the mismatch in both the elastic moduli and yield/tensile strength between the more compliant, and softer crystalline dendrites and the stiffer, stronger BMG matrix promotes nucleation of multiple shear bands during JESSICA A. CLINTON, RACHEL L. MORRISON, and JENNIFER L.W. CARTER are with Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106. Contact e-mail: [email protected] Manuscript submitted December 28, 2015. Article published online April 18, 2017 3220—VOLUME 48A, JULY 2017
loading. Additionally, when the crystalline phase is present at sufficient volume fraction and size, it can prevent the catastrophic proliferation of a single shear band. Although BMGMC’s can promote room temperature ductility, the introduction of the crystalline phase has shown to reduce the elevated temperature ductility exhibited by BMGMC’s as compared to single phase BMC’s. While the introduction of a ductile second phase to the monolithic BMG has been shown to improve the fatigue precracked toughness at temperatures at/below room temperature, the magnitude of the effect is temperature dependent.[10,11] The present work explores the affects of temperature on the tensile and fracture toughness behavior of a toughened BMG that contains Zr-Ti beta-phase dendrites that possess a body-centered cubic (BCC) structure.[12] We attempt to explain the temperature affects by exploring the changes in mechanical performance of the constitutive phases, in particular the crystalline phase. While there is extensive documentation on the effects of test temperature on both tension and toughness of monolithic BCC materials (Nb alloys[13] and Ti alloys[14]), much less work has been conducted to determine the effects of temperature changes on the tensile behavior and toughness of BMGMCs containing such BCC dendrites. First, the paper will discuss the effects of temperature on the tensile behavior of the METALLURGICAL AND MATERIALS TRANSACTIONS A
BMGMCs. Additionally, an analysis of the shape and crystallographic orientation of the BCC dendrites will be presented to explore the cooperative deformation mechanisms between the crystalline and dendritic phases. This combined analysis is used to hypothesize how these cooperative mechanisms can lead to work hardening and so
Data Loading...
