CN1187545A - Method for texture homogenization fining of Ti-Al alloy cast - Google Patents

Abstract

A metallic heat treatment technique for uniformizing and fining the original laminated as-cast structure of Ti-Al alloy castings includes such steps as high-temp thermoisostatic pressure treating in alpha phase region, cyclic heat treating, isothermal treating at eutectoid temp, and treating at critical temp, and features uniformizing and fining whole structure to make it similar to deforming alloy structure, eliminating cast defects, high productivity and low cost.

Description

The method for texture homogenization fining of Ti-Al alloy cast

The invention belongs to the technical field of metal heat treatmet.Be specially adapted to the homogenizing and the refinement of the original as-cast structure of synusia shape of cast ti al alloy.

Intermatallic Ti-Al compound base alloy is the low and hot strength height of a kind of proportion, thereby the high-temperature structural material of potentialization.This material will become and help advanced engine weight reduction, the type material of increasing work efficiency.Through years of researches and exploitation, the room temperature fragility problem of titanium aluminum alloy is resolved substantially by alloying and hot mechanical treatment, adjustment thinning microstructure.In the prior art, because the development and the application of smart casting technology, the development that the right to use gets the titanium aluminum alloy parts is more and more come into one's own.And the original as-cast structure of titanium aluminum alloy is generally thick synusia group, has the holostrome sheet or the nearly holostrome sheet tissue of preferred orientation in various degree.At the processing and treating method that adopts under the thermo-mechanical deformation condition, change the problem of titanium aluminum alloy interior tissue grain refining, be resolved substantially.The method of a kind of titanium aluminium base alloy grain refining of being introduced of Chinese patent ZL93117942.4 for example.This patent is to adopt alloy pig is carried out isothermal forging or hot extrusion pretreatment technology in 900-1250 ℃, carries out recrystallize processing and homogenizing then and handles.In the grain refining treating processes of this patent, pretreated purpose is in order to destroy thick cast structure, therefore adopt the mechanical deformation method of isothermal forging or hot extrusion, reached the purpose that makes the interior thick crystal grain of casting alloy tissue obtain the refinement recrystallize.So this method need to be only applicable to the titanium aluminum alloy member of deformation processing.In the prior art at present,, under the condition of no thermo-mechanical deformation, rely on by thermal treatment and adjust method research with the refinement matrix, still do not have ideal results for the cast ti al alloy foundry goods.

The objective of the invention is to propose a kind of under the condition of no thermo-mechanical deformation, can be effectively the even manufacture method of refinement Ti-Al alloy cast tissue.

To achieve the object of the present invention, the method for the Ti-Al alloy cast homogeneous microstructure refinement that we proposed is Ti-Al alloy cast at first to be placed on carry out the alpha phase zone pyroprocessing in the hot isostatic press, realizes the homogenizing of tissue when eliminating the cast casting defective.Its hot isostatic pressing processing method is that the pressure of isostatic pressing machine is decided to be 120-180Mpa, and Heating temperature is 1380 ℃-1420 ℃, and the soaking time of hip treatment is 10-60 minute.Second step was to carry out 4-8 time cycle heat treatment, and the system of its each cycle heat treatment is 900-950 ℃, is incubated and is warming up to 1150-1200 ℃ again after 1-2 hour, is incubated 0.5-1.5 hour.After the first time, cycle heat treatment finished, with greenhouse cooling to 900-950 ℃, required temperature fall time be 1-3 hour again insulation carry out the cycle heat treatment second time.The 3rd step was to carry out the eutectoid temperature isothermal processes, and its system is Heating temperature 1100-1200 ℃, soaking time 72-120 hour.Carry out critical temperature at last and handle, its temperature is 1320-1380 ℃, soaking time be after 3-15 minute the cold or air cooling of stove to room temperature.

Hip treatment in Ti-Al alloy cast method for texture homogenization fining of the present invention, be when eliminating casting flaw, can make that former primary state cast structure then forms no preferred orientation in the refrigerative process at the alpha phase zone recrystallization, synusia is rolled into a ball the uniform holostrome sheet of size tissue.Its principle is owing to easy diffusion admittances such as dislocation under the High Temperature High Pressure increase, the recrystallization time is shorter, formed α phase crystal grain is less and even, and therefore the holostrome sheet organized layer chip size that makes wants tiny even than the synusia group size that the uniform temp vacuum heat treatment obtains.Adopt the cycle heat treatment method to be because in each cycle heat treatment process, α 2 phases in the titanium aluminum alloy lamellar microstructure or γ all have the free energy of chemistry that makes it that dissolving take place or separate out phase transformation to produce mutually, this energy hunting is the Rayleigh shape disturbance that can aggravate the bedded substance intrinsic, thereby cause bedded substance inner interruption to occur, therefore can in the titanium aluminum alloy lamellar microstructure, introduce end points in the synusia of some amount.Pass through the isothermal thermal treatment of certain hour afterwards, can make the synusia in the cast ti al alloy lamellar microstructure cause the alligatoring reaction that the Gibbs-Thomson effect drives or claim the continuous coarsening reaction, and then to make synusia segmentation isometry be grain-size less than the nearly γ tissue of former synusia group size by inside and outside end points.The nearly γ of the cast ti al alloy that obtains thus organizes closely 150-100 μ m of grain-size.Organizing available metallographic method to measure for the nearly γ that obtains enters _αThe critical temperature T of single phase region _α, and carry out critical temperature and handle.Because in this process, high temperature α/γ synusia structure is to be higher than T _αForm on the γ phase matrix in the temperature section, therefore have four kinds closely be equal to { 111} γ habit plane can be separated out sheet α phase, so the holostrome sheet that forms group size is organized size less than former nearly γ, can reach 120-50 μ m.

Adopt the even thinning method of cast ti al alloy THE STRUCTURE OF CASTINGS of the present invention compared with prior art, can be when no thermo-mechanical deformation, only adopt heat treating method to make the holostrome sheet structure refinement of cast ti al alloy foundry goods, obtain the holostrome sheet and organize synusia group's size and room-temperature mechanical property, near the deforming alloy level.The inventive method and disposable α+γ two-phase region temperature isothermal heat treatment phase compares, the resulting holostrome sheet type that is organized as, and also its synusia group size is littler, more helps temperature-room type plasticity and the toughness and the casting strength of Ti-Al alloy cast.This method only adopts hip treatment in addition, and brought into play simultaneously and eliminated the defective of casting and two effects of homogenizing of tissue, thus improved production efficiency, but also reduced the production technique cost.

Embodiment

The embodiment of the invention is that the employing composition is AL46.5%, Cr1.0%, V2.5%, the material of Ti50% (weight %), the cast moulding Ti-Al alloy cast of in cold crucible vacuum induction shower furnace, smelting, 7 foundry goods of after three remeltings, in copper mold, having cast, each casting dimension is φ 40 * 100mm, then each foundry goods all being adopted wire cutting machine intercepting angle is the 15mm height of 30 ° of ∠, fan-shaped sample, adopt the treatment process of the inventive method and prior art to compare test on these samples again, its comparing result sees the following form.Table 1 is the embodiment of the invention result that compares with the manufacture method of prior art.Table 2 is the comparative result of Ti-Al alloy cast of the present invention and prior art service check.1,2,3,4 for adopting the inventive method to test in table, and 5,6,7 is simultaneous test.The manufacture method comparative result of table 1 embodiment of the invention and prior art

Table 2 Ti-Al alloy cast of the present invention and prior art performance comparison result

Sequence number	Types of organization	Synusia group/grain fineness number μ m	Room temperature strength σ bMPa	Temperature-room type plasticity δ %
					?1	The holostrome sheet	50	?480	?3.1
?2	The holostrome sheet	95	?460	?2.5
					?3	The holostrome sheet	80	?465	?2.6
?4	The holostrome sheet	70	?471	?2.8
					?5	The holostrome sheet	45	?502	?3.5
?6	Bifurcation	150	?410	?2.3
					?7	The holostrome sheet	800	?330	?0.5

Claims (3)

1, a kind of method for texture homogenization fining of cast ti al alloy, this method is Ti-Al alloy cast at first to be placed on carry out the alpha phase zone pyroprocessing in the hot isostatic press, next is to carry out cycle heat treatment, the 3rd step was to carry out the eutectoid temperature isothermal processes, carry out critical temperature at last and handle, it is characterized in that:

A, hip treatment are that the pressure with isostatic pressing machine is decided to be 120-180Mpa, and Heating temperature is 1380-1420 ℃, and the soaking time of hip treatment is 10-60 minute;

The temperature of B, each cycle heat treatment is that 900-950 ℃ of insulation is warming up to 1150-1200 ℃ after 1-2 hour again, and soaking time is 0.5-1.5 hour;

C, the Heating temperature of carrying out the eutectoid temperature isothermal processes are 1100-1200 ℃, soaking time 72-120 hour;

The Heating temperature that D, critical temperature handle is 1320-1380 ℃, soaking time be after 3-15 minute the cold or air cooling of stove to room temperature.

2, cycle heat treatment system according to claim 1 is characterized in that after cycle heat treatment finishes for the first time, and when cooling the temperature to 900-950 ℃, required temperature fall time is insulation again in 1-3 hour.

3, according to claim 1,2 described cycle heat treatment systems, the cycle index that it is characterized in that cycle heat treatment is 4-8 time.