NiAl-Based microstructurally toughened composites
- PDF / 1,750,825 Bytes
- 7 Pages / 597.6 x 774 pts Page_size
- 87 Downloads / 179 Views
I.
INTRODUCTION
THE intermetallic NiAI has been the subject of considerable research as a result orits exceptional stiffness-todensity ratio, high melting point, oxidation resistance, and potential for high-temperature strengthening. l1 ,21 However, the very low room-temperature ductility and toughness of NiAI has prevented its use in structural applications. Unlike its Ni3Al counterpart which can be successfully ductilized by the addition of boronpl efforts to alloy NiAI to improve room-temperature ductility and toughness have been unsuccessful. The current work was aimed at producing NiAI base composites with significantly improved room-temperature toughness and structural reliability. The basic measure used to assess structural reliability in the current study is the energy absorbed by the composite during notched Charpy impact testing. The approach investigated to increase the composite energy absorption capability involved incorporating continuous ductile toughening networks throughout the NiAI base matrix. Composites produced in such a manner are referred to as microstructurally toughened (MT*) composites in the remain*MT is a service mark of United Technologies Corporation, East Hartford, CT.
der of the paper. The tensile and notched Charpy impact behavior of a number of MT NiAI base composites are presented and discussed below.
II. MATERIALS AND EXPERIMENTAL PROCEDURE The MT composites investigated in this study consisted of continuous tubular 304 stainless steel toughening regions embedded within a matrix of boron carbide
VINCENT C. NARDONE, Senior Research Scientist, and JAMES R. STRIFE, Principal Scientist, are with United Technologies Research Center, E. Hartford, CT 06108. Manuscript submitted May 10, 1990.
METALLURGICAL TRANSACTIONS A
particulate (B 4C)-reinforced NiAi. A representative cross section of a MT B4 C/NiAl/304 composite is shown in Figure 1. The 304 stainless steel occupied 40 vol pct of the microstructure for all composites. The reinforced region consisted of 25 vol pct B4 C in NiAI. The increase in density resulting from the addition of the 304 stainless steel was compensated by a decrease in density associated with the addition of the B4 C so that the overall composite density was within 5 pet of the value for monolithic NiAI. Composites were fabricated with varying outer diameters (00) and wall thicknesses of the 304 tubular regions. In addition, composites were fabricated with two reinforced/toughening region interfacial conditions designed to promote different degrees of crack front deflection during notched Charpy impact testing. A summary of the composites fabricated for evaluation is provided in Table I. All of the composites were evaluated in the as-fabricated condition. The tensile specimen geometry consisted of 1O.2-cmlong button head specimens with a nominal O.64-cm gage diameter and a 3.0-cm gage length. Testing was performed at a constant crosshead speed of 0.127 cm/min. For the room-temperature testing, strain was monitored using strain gages bonded to opposite sides
Data Loading...
