Metal treatment – Stock – Aluminum base
Reexamination Certificate
2001-04-04
2003-09-23
King, Roy (Department: 1742)
Metal treatment
Stock
Aluminum base
C148S337000, C075S338000, C164S046000, C164S097000
Reexamination Certificate
active
06623571
ABSTRACT:
The present invention relates to metastable aluminium-titanium materials and to a process for their manufacture.
In recent times the continuing and rapid advancement in technology has led to the design and development of high performance devices capable of operating in increasingly hostile service conditions. From the existing trend in the technological development it can be anticipated that the severity of the service conditions that these devices will have to withstand will increase in the time to come. One of the important criterion to realize the continuing improvement in the efficiency of these devices is the development of materials that will be used to make these devices and their ability to withstand increasingly hostile service conditions. Aluminium alloys with titanium as the main alloying element are one such class of materials actively pursued for possible application in relatively high temperature and high stress conditions.
The use of titanium in aluminium has been explored as an alloying element so as to synthesize high performance materials for advanced engineering applications. Processing techniques based on molten metals (such as conventional casting and spray atomization and deposition) and metallic powders (such as powder metallurgy and mechanical alloying) have been investigated. Amongst these techniques, the synthesis of aluminium-titanium materials can be carried out more cost effectively by the methods based on molten metals. The studies conducted so far have shown that the addition of titanium in the liquid aluminium leads to: a) an increase in the melting temperature of aluminium significantly and b) reaction between titanium and aluminium to form Al
3
Ti through peritectic reaction. For example, addition of 10 weight percent of titanium in aluminium raises the melting point of aluminium from ~660° C. to ~1200° C. besides significantly increasing the chemical reactivity of the resultant molten Al—Ti mixture. This necessitates the use of more expensive and specialised furnaces (such as induction furnace) capable of heating to higher temperatures and crucibles made of highly inert materials thus increasing the overall cost of synthesis material. The interaction between titanium and aluminium in the molten condition results in either a solid solution of titanium in aluminium (with very limited solid solubility) or the formation of Al
3
Ti through peritectic reaction or primary solidification. The microstructures of aluminium-titanium synthesized using conventional casting with slow cooling rate and spray atomization and deposition with reasonably high cooling rates (~10
3-4
K/s) revealed the as-expected existence of Al
3
Ti intermetallic phase and equilibrium/extended solid solubility of titanium in aluminium. Neither of these techniques has shown the capability of synthesizing aluminium-titanium materials at temperatures lower than that exhibited by equilibrium Al—Ti phase diagram and in retaining the titanium as titanium in its elemental form following solidification by controlling the reaction between the molten aluminium and titanium.
We have now found a process for producing metastable aluminium-titanium materials which may be successfully produced at temperatures lower than those required by the equilibrium Al—Ti phase diagram. The metastable aluminium-titanium materials have been produced by controlling the reaction of the titanium with the molten aluminium in order to retain a proportion of the titanium in its elemental form.
According to the present invention there is provided a process for the manufacture of a metastable aluminium-titanium material comprising the steps of:
i) melting aluminium in a crucible;
ii) mixing solid particulate titanium with the molten aluminium; and
iii) disintegrating or spraying the molten mixture on a metallic substrate such that the molten mixture is deposited and solidified on the metallic substrate,
and wherein at least a substantial portion of the titanium is retained as elemental titanium after the molten mixture is solidified on the metallic substrate.
There is also provided a metastable aluminium-titanium material manufactured by the process described in the immediately preceding paragraph.
It will be understood that by the term “at least a substantial portion of the titanium is retained as elemental titanium” it is meant that sufficient elemental titanium is present in the metastable titanium material to strengthen the aluminium matrix. The presence of titanium in the matrix advantageously serves to improve the mechanical behaviour of the aluminium at ambient and elevated temperatures as a result of its high melting point, strength and modulus properties. If not for the presence of metastable titanium in the matrix and associated metastable strengthening, the synthesis requirement for conventional Al—Ti alloys with similar amounts of titanium in the form of precipitates or in solid solution will necessitate a much more complex combination of melting process (skull melting), furnaces (induction furnace), crucible (titanium) and superheating temperatures. As an example, synthesis of Al with 10 wt. % Ti will require a superheat temperature of ~1200° C. when compared to 750° C. using the presently described process. It is preferred that the elemental titanium retained in the metastable aluminium-titanium material is present in an amount ranging up to 20% by weight of the material.
It is preferred that the retained elemental titanium in the particulate form is uniformly distributed throughout the material. The uniform distribution indicates a non-aligned and non-clustered (as much as possible) distribution in three directions (an isotropic distribution).
In a preferred embodiment, the mixture of molten aluminium and particulate titanium is poured or allowed to flow from the crucible, and is subsequently disintegrated using jets of inert gas, the spray from the disintegrated mixture being deposited and solidified on the metallic substrate.
The at least a substantial portion of the titanium may be retained as elemental titanium by controlling the exposure time of the titanium to the molten aluminium. The period will be readily determined by simple experimentation having regard to the temperature of the aluminium to which the titanium is exposed and the particle size of the solid particulate titanium. The lower the temperature of the molten aluminium, the longer the treatment period which the titanium may be exposed to the hot aluminium. The larger the particulate size of the solid particulate titanium, the longer the treatment period which the titanium may be exposed to hot aluminium. The emphasis however is to advantageously minimize the exposure time of the particulate titanium to the molten aluminium so as to avoid undesirable reactions between the two and to enhance the retention of the elemental titanium by aluminium following solidification.
The solid particulate titanium may alternatively or additionally be treated prior to mixing with the molten aluminium in order to increase the period the titanium may be exposed to the hot aluminium and to enhance the retention of elemental titanium in aluminium following solidification. For example, the solid particulate titanium may be treated to produce an oxide coating thereupon so as to decrease the reactivity of the solid particulate titanium to the molten aluminium. Titanium powders may be preheated to temperatures in the range of from 600° C. to 815° C., preferably about 650° C. for a period of at least 30 minutes, preferably 1 hour in order to produce an oxide surface layer.
The present invention further provides a metastable aluminium-titanium material, of which a substantial portion of the titanium comprises solid particulate titanium which is substantially uniformly distributed throughout the aluminium.
The metastable aluminium-titanium material comprises the presence of nearly uniformly distributed elemental titanium particulates in a non-aligned and non-clustered form in all three directions, with minimal reaction with the aluminium based matrix. The mate
King Roy
National University of Singapore
Wessman Andew
LandOfFree
Metastable aluminum-titanium materials does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Metastable aluminum-titanium materials, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Metastable aluminum-titanium materials will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3063758