Notch Effects on Room Temperature Tensile and Bend Properties of Ni 3 Al and Ni 3 Al+B
- PDF / 3,009,683 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 15 Downloads / 259 Views
NOTCH EFFECTS ON ROOM TEMPERATURE TENSILE AND BEND PROPERTIES OF Ni 3 Al AND Ni 3AI+B P. S. KHADKIKAR, J. D. RIGNEY, J. J. LEWANDOWSKI AND K. VEDULA Department of Materials Science and Engineering Case Western Reserve University Cleveland, Ohio 44106
ABSTRACT The notched mechanicalproperties of Ni3 AI and Ni5 AI+B prepared by powder metallurgy techniques have been determined in both tension and bending at room temperature. Ten8ile tests performed using double notched specimens containing relatively blunt notches produced intergranular fracture in both Ni 3 Al and Ni3AI+B, with evidence of fracture initiating in an intergranular manner ahead of the blunt notch in both cases. Estimates of notched fracture toughness from bend tests and of local grain boundary fracture stress from the notched tensile tests suggest an increase in these values with boron addition.
1 INTRODUCTION The discovery of the beneficial effects of boron addition on the smooth tensile behavior of Ni 3AI [1,2] has resulted in a considerable research effort in this area. However, the effects of stress concentrations on the mechanical behavior of Ni 3AI and Ni 3AI+B are less well characterized. Recent work [3] has indicated that Ni 3 AI+B is notch sensitive at room temperature, although the details of the notch geometry and the subsequent fracture modes were not given. In an attempt to induce intergranular fracture in Ni 3 AI+B to enable Auger spectroscopy of grain boundaries, Liu et al. (2] fractured notched Auger specimens in high vacuum. Their effort was apparently unsuccessful, as subsequent efforts utilized hydrogen pre-charging prior to fracture. The present study was undertaken to characterize the effects of a well defined notch on both tensile and bend bar tests at room temperature. Blunt-notched tensile specimens were employed to study the effects of a moderate stress concentration on fracture behavior of Ni 3 AI and Ni3AI+B, while estimates of the local grain boundary fracture stresses were obtained using existing stress analyses. Both sharp notched and fatigue precracked specimens were tested to estimate the effects of boron on the toughness of these materials. 2 EXPERIMENTAL PROCEDURES The alloys investigated were prepared by either hot extrusion or vacuum hot pressing of prealloyed Ni 3 AI powder (-80+325 mesh) obtained from Alloy Metals, Inc. , Troy, MI. Boron was added in elemental form via blending in a Vee-blender. Both hot extrusion (1400 K, area reduction ratio of 16:1) and hot pressing (1323 K, 4 h, 48 MPa) resulted in fully dense materials. Tensile specimens containing two blunt notches (root radius = 0.32 mm ) were machined via centerless grinding from the extruded material. Double notched specimens were employed to enable identification of microstructural features associated with fracture initiation [5]. In double notched specimen tensile tests, the notch that remains in-tact after testing to failure represents a specimen unloaded just prior to catastrophic fracture. These unbroken notches were longitudinally sectioned and met
Data Loading...
