Materials Week '97: Wednesday PM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Wednesday afternoon, September 17.

MICROSTRUCTURE PROPERTY RELATIONSHIPS IN / TITANIUM ALLOYS: Session III: Mechanical Properties

Session Chair: Neville Moody, Sandia National Labs, P.O. Box 969, Division 8312, Livermore, CA 94551-0969

RELATIONS BETWEEN MIICROSTRUCTURE AND PROPERTIES IN TITANIUM ALLOYS: Anthony W. Thompson, ESRC, University of California, Berkeley, CA 94720

The role of microstructural variables in controlling mechanical properties of alpha-beta titanium alloys has been well explored. For tensile, toughness and fatigue properties, there are a number of generalizations which appear appropriate; the same is true to a lesser extent for environmental properties. However, there are several unsolved problems in these relationships, which can largely be characterized as examples of the "two ductile phases" problem. The current status of these problems is the basis for recommendations of additional research.

2:40 pm

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF TITANIUM CASTINGS: G. Wegmann, J. Albrecht, G. Lütjering, Technical University Hamburg-Harburg, D-21071 Hamburg, GERMANY; K.D. Folkers and Ch. Liesner, Titan-Aluminum-FeinguSS GmbH, D-59909 Bestwig, GERMANY

The demand for the use of titanium for aircraft applications has been increased over the past years by the necessity for weight reductions for improved fuel economy. Due to the high cost of titanium, the use of investment cast parts receives an increasing interest due to the large cost saving potential of this technology in manufacturing the part. Contrary to forged material, however, the possibilities to optimize the properties via microstructural control are limited for cast parts to purely thermal treatments. This paper discusses the possibilities to modify the lamellar structure of cast Ti-alloys by heat-treatment in the + phase field, followed by controlled cooling. By this treatment, the -phase can be hardened by the precipitation of very fine -lamellae, resulting in a so-called "bi-lamellar" microstructure. It was shown that bi-lamellar microstructures have improved yield stress, creep and fatigue resistance as compared to conventional lamellar (as-cast) microstructures. The influence of the processing parameters, i.e. +-annealing temperature and subsequent cooling rate as well as the cooling rate during casting, on the mechanical properties of cast Ti-6Al-4V and Ti-6242, will be discussed on the basis of the microstructural parameters.

3:00 pm

PROPERTIES OF ALPHA-BETA TITANIUM ALLOYS AT THE SUBMICRON SCALE: N.R. Moody, C. Cadden, Sandia National Laboratories, Livermore, CA 94550; A.W. Thompson, University of California, Berkeley, CA 94720; D. Allen, University of Florida, Gainesville, FL 32611

The full potential for the use of alpha-beta titanium alloys is limited by our understanding of how the properties of each microstructural phase contribute to the properties of the alloy. We are therefore using nanoindentation to measure the elastic modulus and hardness of individual phases in alpha-beta titanium alloys at the submicron scale. This technique has been used to study the variation in elastic modulus and hardness across a weld zone of a titanium aluminide alloy. It has also been used to study the effects of hydrogen on the elastic modulus and hardness of individual phases in another alloy of similar composition. These results will be discussed in this presentation and compared with properties of the parent alloys to help define the contributions of constituent phases to alloy properties. This work supported by U.S. DOE Contract DE-AC04-94AL85000.

3:20 pm

RHEOLOGICAL ASPECTS OF THE SUPERPLASTICITY OF Ti-6Al-4V: Michael L. Meier, Amiya K. Mukherjee, Department of Chemical and Materials Science, University of California at Davis, Davis, CA 95616

The full potential for the use of alpha-beta titanium alloys is limited by our understanding of how the properties of each microstructural phase contribute to the properties of the alloy. We are therefore using nanoindentation to measure the elastic modulus and hardness of individual phases in alpha-beta titanium alloys at the submicron scale. This technique has been used to study the variation in elastic modulus and hardness across a weld zone of a titanium aluminide alloy. It has also been used to study the effects of hydrogen on the elastic modulus and hardness of individual phases in another alloy of similar composition. These results will be discussed in this presentation and compared with properties of the parent alloys to help define the contributions of constituent phases to alloy properties. This work supported by U.S. DOE Contract DE-AC04-94AL85000.

3:40 pm

THE FIBRE-MATRIX INTERFACIAL REGION OF TITANIUM MATRIX COMPOSITES AND ITS EFFECT ON FATIGUE CRACK GROWTH RESISTANCE: S.V. Sweby, P. Bowen, and M. Strangwood, The University of Birmingham, School of Metallurgy and Materials, Elms Road, Edgbaston, Birmingham,B15 2TT, UK

Ti-6Al-4V (wt.%) continuously reinforced with SM1140+ or SM1120 fibers has been characterized in the as-processed condition and after heat treatment above the -transus. The nature of the interface between matrix and fibers, as well as the matrix microstructure, has been characterized by SEM and TEM. These results have been related to fiber push-out tests for material in both conditions, which, with single fiber strength results, have been used to rationalize variations in fatigue crack growth resistance as a function of heat treatment.