METHOD OF MAKING TITANIUM ALLOY BASED AND TiB REINFORCED COMPOSITE PARTS BY POWDER METALLURGY PROCESS

Abstract

A method of preparing a titanium-based metal matrix composite. In one form, titanium hydride can be added to substantially pure titanium, an alloying material and a source of boron such that a mixture of these materials can be compacted and sintered in a powder metallurgy process to produce a component made up of a titanium boride reinforced titanium alloy. In another form, the substantially pure titanium, alloying material and source of boron could be vigorously mixed (with or without the titanium hydride) to such an extent that oxide films that may have built up on the titanium precursor can be removed to minimize the presence of oxygen in the manufactured component.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates generally to ceramic-reinforced metal alloys, and more particularly to titanium boride-reinforced titanium alloys and methods of making such alloys.[0002]Powder metallurgy (PM) is a popular way to produce components from a wide range of materials, many of which are difficult or impossible to produce by more conventional approaches, such as casting, forming or machining. PM is particularly well-suited to making components from both refractory materials as well as materials that in other processes that do not permit the formation of a true alloy, and is especially beneficial in high-volume production (such as automobile component manufacturing) due to its repeatability and scrap avoidance attributes.[0003]In a typical PM process, a metal powder is mixed with alloying materials, lubricants, binders or the like, pressed into a near-net shape with appropriate tooling, then sintered in a controlled atmosphere to metallurgicall...

AI Technical Summary

Benefits of technology

[0013]In another option, the process of mixing can serve two purposes. In addition to the primary benefit of evenly distributing the powder or other constituents, the inventors have determined that a more aggressive mixing approach helps to strip away oxide layers that may have built up on the surface of the titanium during the exposure of the metal to the atmosphere or related oxygen-containing environment. In this way, the mixing further comprises removing at least a portion of such oxygen-based material. More particularly, the removing comprises placing the precursor materials in an inert environment (for example, argon after oxygen evacuation) and subjecting them to rotational mixing until such time as the mixed materials have predetermined characteristics, such as a maximum powder size, surface smoothness, evidence of pre-sintering alloying, as well as tap density increases, where the latter corresponds to the bulk density of the mixed material after having been shaken or compacted to promote settling. The rotational mixing may more specifically include using rotational speeds of agitators, a mixing drum or other mixing member at high rotational speeds for extended lengths of time. The inventors have found that rotational speeds of approximately 3600 revolutions per minute for between approximately four and twelve hours produces the degree of mixing necessary to effect one of the aforementioned predetermined characteristics, oxygen film removal, or both.

[0015]In addition to the mixing, compacting and sintering operations discussed above, other optional steps may be undertaken. For example, one or more surface-modifying operations, such as deburring, surface compressive peening, porosity reduction or impregnation (the last to introduce lubricants into the component such as may be used in bearings, journals or related friction-reducing parts), may be undertaken to improve the functionality of the finished component.

Problems solved by technology

Nevertheless, its limited stiffness has made it hitherto difficult to fully exploit the advantages titanium has to offer relative to its more refractory counterparts.

The use of additional quantities of material to compensate for these lower stiffness values reduces the efficiency advantages that titanium enjoys over nickel and iron based alternatives.

Nevertheless, TiB is unstable by itself, so it has to be produced in situ, such as through reaction of titanium diboride (TiB2) with titanium powder during sintering.

There are many challenges associated with the production of titanium-based MMCs by powder metallurgy.

The presence of such oxygen can result in lower density and mechanical properties in the final product, by limiting the production of the more desirable reinforcing phases such as the aforementioned diboride.

Images