Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
DUCTILE TITANIUM ALLOY MATRIX FIBER REINFORCED COMPOSITES
Document Type and Number:
WIPO Patent Application WO/1994/023077
Kind Code:
A1
Abstract:
A titanium alloy matrix fiber reinforced composite made from titanium alloy sheet processed to have ductility up to about 35 %. Of particular usefulness is the composite having a Ti3A1 titanium aluminide having this level of ductility. The composites have good resistance to thermal cyclic fatigue. Preferred reinforcing fibers are silicon carbide. The processing involves multiple working steps below the beta transus with intervening thermal annealing steps, also at temperatures below the beta transus.

Inventors:
Linsey, Gary D.
Chen, Otis Y.
Blackburn, Martin J.
Application Number:
PCT/US1994/002681
Publication Date:
October 13, 1994
Filing Date:
March 14, 1994
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
UNITED TECHNOLOGIES CORPORATION.
International Classes:
C22C49/00; C22C14/00; C22C47/00; C22C49/11; C22C49/12; (IPC1-7): C22C1/09; C22C14/00; B32B15/00
Foreign References:
US5118025A1992-06-02
Other References:
DATABASE WPI Week 8926, Derwent World Patents Index; AN 89-190079
S.C. JHA; J.A. FORSTER; A.K. PANDEY; R.G. DELAGI: "TITANIUM-ALUMINIDE FOILS", ADVANCED MATERIALS & PROCESSES, vol. 139, no. 4, 1991, pages 87 - 90
Download PDF:
Claims:
Claims
1. A titanium alloy matrix fiber reinforced composite material comprising at least one layer of high strength reinforcing fibers embedded in a matrix o Ti3Al material, said matrix material having at least 10% room temperature ductility and improved resistance to thermal cyclic fatigue.
2. A composite material as recited in claim 1 wherein said matrix material has at least 20% room temperature ductility.
3. A composite material as recited in claim 1 wherein said matrix material has at least 35% room temperature ductility.
4. A composite material as recited in claim 1 wherein said reinforcing fibers are of silicon carbide.
5. A composite material as recited in claim 1 wherein the volume of reinforcing fibers in the composite is a maximum of about 40%.
6. A composite material as recited in claim 1 wherein the volume of reinforcing fibers in the composite is about 30%.
7. A composite material as recited in claim 1 wherein the titanium alloy is of the Ti3Al titanium aluminide type.
Description:
Description

Ductile Titanium Alloy Matrix Fiber Reinforced

Composites

Technical Field

This invention relates to a fiber reinforced composite material with a titanium alloy-based matrix, and more particularly to a titanium aluminide intermetallic compound-based matrix fiber reinforced composite or titanium alloy matrix fiber reinforced composite material wherein the matrix material has good ductility at room temperature.

Background Art

The uses of materials in aircraft gas turbine engines have become increasingly demanding in recent years. The requirements of increased performance and decreased fuel consumption place a premium on high strength and light weight. Improved performance generally relates to increases in operating temperature, so that material strengths must be retained at higher temperatures than previously encountered.

Titanium alloys generally provide high strength with light weight, although their useful strength is limited to approximately 1000°F, and special precaution must generally be taken to prevent oxidation. Titanium aluminideε, generally of the TiAl or Ti 3 Al type, retain useful properties up to about 1500°F, but their usefulness is limited because their low temperature ductility greatly limits the fabrication techniques which may be used, and makes them highly susceptible to matrix cracking due to mechanical damage incurred durin normal handling and usage at ambient temperature. It is well known to increase the strength of structural materials by embedding high strength fibers in a matrix material to form composite materials. Whil these composite materials generally benefit by combinin the best properties of the component materials, such as the high strength of the reinforcing fibers, they can also be limited by other properties of the materials. Titanium alloy fiber reinforced composites have improved strengths, but are still limited by the high temperature strength and low oxidation resistance above 1000°F. Titanium aluminide matrix fiber reinforced composites also have improved strength, with the improvements being retained up to 1500°F. Fabricabilit of the titanium aluminide fiber reinforced composites i

very limited because of the low room temperature ductility of the titanium aluminide.

In U.S. Patent 4,816,347, to Rosenthal, et al., this limitation of low room temperature ductility was overcome by interposing layers of a titanium alloy having good ductility, positioned to surround the high strength reinforcing fibers, between sheets of titanium aluminide, thus providing a hybrid titanium metal matri composite having good strengths at temperatures up to about 1500°F and good room temperature mechanical properties including good ductility and improved resistance to matrix cracking.

The improved high temperature' strength of a titanium aluminide matrix fiber reinforced composite material is generally accompanied by limited fabricability due to low room temperature ductility. Rosenthal, et al., were able to resolve this problem only by the addition of a lower strength titanium alloy material, thus forming a hybrid composite. The additio of the lower strength material, however, results in a reduction in the overall capabilities of the composite. Siemers, in U.S. Patent No. 4,786,566, disclosed a method for formation of a fiber reinforced trititanium aluminide matrix composite which involves plasma spraying of the matrix material onto an array of aligne fibers to form a fiber reinforced sheet. The sheets ar

then laid up and bonded together to form a fibet reinforced object. Siemers reported that the composite had good strength, but that the ductility was somewhat limited. This technique avoids the difficulties associated with trying to form thin sheets of the low ductility titanium aluminide material, but does not provide composites which are particularly usable.

Composites made without the ductile matrix suffer performance deficits during such tests as thermal fatigue cycling, where the component is exposed to temperatures ranging, generally, from room temperature to an elevated service temperature. Large stresses are generated in the boundary region at the interface between the fibers and the matrix, due to the large mismatch in the thermal expansion coefficients of the reinforcing fibers (2.7 x 10 '6 /°F for SCS-6 silicon carbide fibers, a product of Textron Specialty Metals/Subsidiary of Textron, Inc.) and the matrix material (5.7 x 10 "6 /°F for Ti 3 Al. These stresses frequently cause cracking in the matrix, and/or disbonding of the reinforcing fibers from the matrix, which leads directly to failure of the composite.

Thus, what is needed is a material which achieves the good high temperature strength properties of a titanium aluminide matrix fiber reinforced composite material while retaining good low temperature ductility.

Disclosure of the Invention

This invention provides a fiber reinforced composite material wherein the matrix material, either titanium alloys or titanium aluminide-based intermetallic compounds, has improved ductility at room temperature compared to conventionally processed matrix materials. A unique processing technique, involving thermomechanical processing which includes multiple working steps below the beta transus with intervening thermal annealing steps, also at temperatures below the beta transus, provides matrix materials having reduced elastic modulus and ductilities up to about 45%.

Fiber reinforced composites based on these improve matrix materials can be formed at temperatures lower than the temperatures conventionally used for titanium matrix composite formation, which reduces the formation of oxides and other undesirable brittle compounds at th fiber-matrix interface. The resulting composites experience a significant reduction in the amount of matrix cracks generated in the matrix and at the fiber- matrix interface during thermal cycling tests.

These, and other features and advantages of the invention, will be apparent from the description below, read in conjunction with the drawings.

Best Mode for Carrying Out the Invention

The invention process involves the formation of a fiber reinforced composite material having a matrix of either Ti 3 Al or a titanium alloy, with the matrix material being processed to provide enhanced ductility and reduced elastic modulus.

The high ductility, low modulus Ti 3 Al base matrix material is obtained by subjecting the material to a series of hot rolling steps at temperatures below the beta transus temperature for the particular alloy, whic is typically about 2000°F for most titanium alloys. In hot working, especially rolling, the material cools during processing. The hot rolling in the invention process is initiated at about 1600-1800°F, and proceeds until the material cools to about 1100-1400°F, at which point the material is reheated and rolled further. At the completion of rolling, a 1-10 hour anneal at about 1600-1900"F is preferred. In this manner, very thin sheets, on the order of 0.020" thick, can be produced having room temperature ductilities of at least 10%, an in many cases up to as high as 45%. The material also has a reduced elastic modulus compared to conventionall processed material. This material may then be cold rolled to further reduce the thickness, and intermediat sub-beta transus anneals may be employed to relieve the residual stresses built up during the cold rolling.

This procedure is explained in further detail in U.S. Patent Application Serial No. 07/239,484, of common assignee herewith, which is currently subject to a USPT secrecy order, and which is incorporated herein by reference.

Similar thermomechanical processing as was applied to the Ti 3 Al inter etallic compound material can also be applied to other titanium alloys with similar increases in ductility, both at room temperature and at elevated temperatures, while basically retaining the other significant mechanical properties.

A composite is formed by positioning reinforcing fibers, arrayed in a manner suitable for the intended application, between sheets of the matrix material. Th desired composite structure is achieved by assembling a series of properly oriented layers of the fibers betwee matrix material sheets until the desired thickness and configuration are achieved.

The assembly is then compacted under conditions of applied pressure at elevated temperature, allowing the sheets of matrix material to deform and surround the reinforcing fibers, followed by diffusion bonding of th individual sheets of the matrix material to form a continuous matrix around the reinforcing fibers. In this manner, a composite is formed which combines the strength properties of the reinforcing

fibers with the enhanced ductility of the matrix material. The mechanical properties of the composite material are adequately predicted by the Rule of Mixtures, which is commonly applicable to composite materials.

Thus titanium alloy matrix fiber reinforced composite materials can be formed at lower temperatures using these enhanced ductility materials, which reduces the susceptibility of the materials to undesirable high temperature effects, such as brittle compound formation at the fiber-matrix interface, during consolidation of the matrix around the fibers.

The principles of the present invention may be better understood through reference to the following illustrative examples.

Example 1 High ductility, low modulus alpha-two (Ti-14A1- 23Nb-2.2V) foil was prepared using the rolling techniques described in Patent Application Serial No. 07/239,484, referred to above. A single layer of SCS-6 silicon carbide reinforcing fibers (a product of Textro Specialty Metals, a subsidiary of Textron, Inc.) was then laid up so that the fibers were parallel to each other and uniformly spaced approximately one fiber diameter from each other. A layer of the ductile foil was then laid over the layer of fibers. In a similar

manner additional alternating layers of fibers and foil were laid up until the desired thickness of eight layer was achieved. This composite had about 30% by volume o fiber in the matrix, although we believe, based on our experience with other similar composite materials, that this invention will work as well with fiber volumes up to about 40%.

This fiber-foil assembly was then placed in a vacuum hot press, and the assembly was subjected to a pressure of 5 ksi at a temperature of 1750°F for a period of 10 minutes, 10 ksi at 1750°F for 10 minutes, and 15 ksi at 1750°F for 160 minutes. The composite produced in this manner had a strength of 230 ksi and a modulus of elasticity of 30,000,000 psi, which is as predicted by the Rule of Mixtures.

Metallographic examination of the composite revealed full consolidation without chemical reaction between the fibers and the matrix material. Adequate thermal fatigue resistance was demonstrated by exposing the composite to 100 cycles between room temperature an 1500°F, after which no longitudinal or transverse cracking in the matrix material between the fibers was observed metallographically.

Example 2 Ductilized alpha-two (Ti-14Al-21Nb) foil was prepared using the same rolling techniques as in Exampl

1. A single layer of SCS-6 silicon carbide reinforcing fibers was then laid up so that the fibers were paralle to each other and uniformly spaced approximately one fiber diameter from each other. A layer of the ductile foil was then laid over the layer of fibers. Again additional alternating layers of fibers and foil were laid up until the desired thickness of eight layers was achieved. About 30% by volume of fiber in the matrix was achieved. This fiber-foil assembly was then placed in a vacuum hot press, and the assembly was subjected to a pressure of 5 ksi at a temperature of 1800°F for a period of 10 minutes, 10 ksi at 1800°F for 10 minutes, and 15 ksi at 1800°F for 160 minutes. The composite produced in this manner also had a strength of 230 ksi and a modulus of elasticity of 30,000,000 psi.

Metallographic examination of the composite revealed full consolidation without chemical reaction between the fibers and the matrix material. Adequate thermal fatigue resistance was demonstrated by exposing the composite to 100 cycles between room temperature an 1500°F, after which no longitudinal or transverse cracking in the matrix material between the fibers was observed metallographically. A similar composite, prepared of Ti-14Al-21Nb and

SCS-6 fibers, but using the plasma spray technique for

forming the matrix material around the reinforcing fibers described in Siemers, experienced both longitudinal and transverse cracking of the matrix material, as determined metallographically. Although this invention has been shown and described with respect to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.