CN105603533A - Alloy design method for reducing directionally-solidified titanium aluminum alloy interface reaction - Google Patents

Abstract

The invention discloses an alloy design method for reducing directionally-solidified titanium aluminum alloy casting member and casting mold coating interface reaction, and belongs to a method for improving titanium aluminum alloy casting quality. The specific steps are as follows: designing TiAl alloys with different Nb contents for directional solidification process to obtain casting members; and using a microhardness tester to test Vickers microhardness to determine interface reaction layer thickness. A German brooke Quantax400-10 energy dispersive spectrometer is used for sample interface element distribution analysis, a German Brook D8AdanceX ray diffractometer is used for sample surface phase analysis, and a United States FEIQuanta TM250 scanning electron microscope is used for casting memberreaction layer and casting member matrix tissue morphology observation and analysis. Through corresponding analysis and test of the directionally-solidified titanium aluminum alloy casting members obtained by the alloy design, interfacial reaction degree can be obtained specifically and vividly, corresponding titanium aluminum alloy casting member quality can be well evaluated, and a TiAl alloy casting member with optimized Nb content can be obtained.

Description

A kind of alloy design method that reduces directionally solidifying titanium aluminum alloy interfacial reaction

Technical field

The design has studied a kind of directionally solidifying titanium aluminum alloy foundry goods and alloy design method that casting mold coating interface reacts of reducing, and belongs to the method for improving titanium-aluminium alloy castability.

Background technology

TiAl alloy density is low, specific strength is high, specific stiffness is high, good heat resistance, there is high Properties of High Temperature Creep and oxidation resistance, it is the best lightweight high temperature alloy of combination property, be the preferred material of superelevation velocity of sound aircraft and advanced aero engine of future generation, therefore become the emphasis of studying in alloy in lightweight.

At present, most of PM technique, casting and the ingot metallurgy technology of adopting of TiAl base alloy produced. TiAl is compound between a kind of brittle metal. The TiAl alloy at present actual biggest obstacle using is brittleness at room temperature and the difficult deformation processing of this compound. Therefore, foundry engieering is just replacing ingot metallurgy and forging process technology, day by day becomes the main flow that TiAl alloy industryization is produced. Casting TiAl alloy is reliably technically, and academia and industrial quarters think that doing in design the rear TiAl base alloy of some adjustment can replace nickel-base alloy for some engine components.

Researcher mainly concentrates on eye on TiAl base alloy precision foundry engieering. Precision casting technology is the forming technique that applies to the earliest TiAl base alloy. It mainly comprises model casting and die cast, and the former is mainly for the preparation of complex-shaped TiAl base alloy component, and latter is for the preparation of shape matching rule, parts that output is large. Adopt investment precision casting technology to prepare TiAl base alloy components and can shorten the manufacturing cycle, reduce material consumption, and can adopt wax-pattern packaging technology entirety essence to cast out the assembly of multiple members, be usually used in the shaping of complicated Aero-Space, auto industry heat-resistant component, the method can obtain the accurate complex component without surplus or Near net shape, and manufacturing cost significantly declines compared with machining. But the shortcomings such as foundry goods exists, and grain structure is thick, intensity is lower, alloy graining shrinks greatly and solidified structure loosens. Directional solidification technique can be eliminated transverse grain boundaries and obtain fine and close tissue, puies forward heavy alloyed creep rupture strength and plasticity, improves thermal shock drag and creep strength, has extremely important and application widely in industry and high-tech sector. Adopt the TiAl alloy-steel casting prepared of directional solidification technique because microscopic structure obtains remarkable refinement and aligns, thereby increase substantially the service ability of TiAl alloy components.

Interfacial reaction between TiAl alloy and casting mold is ubiquitous problem in TiAl alloy casting process. In TiAl Alloys Casting process, because the alloy of melting has very high chemism, react in when cast and casting mold coating material, produce a series of casting flaw, as cast(ing) surface pollution layer, pore, pin hole, shrinkage porosite etc., inside and the surface quality of titanium alloy casting that these defects are deteriorated, affects the dimensional accuracy of foundry goods, has directly affected the quality and performance of foundry goods; Meanwhile, the existence of directional solidification process median surface reaction also can form pollution layer at cast(ing) surface, destroys the continuous growth of column crystal, changes the direction of growth of crystal, weakens the mechanical performance of directional solidification castings. Therefore, the interfacial reaction between TiAl alloy melt and mo(U)ld face is studied, grasped the reaction mechanism at TiAl alloy melt and casting mold interface, find its rule, and then control the interfacial reaction degree of titanium alloy and mold material. This to producing the TiAl alloy of high-quality, the overall strength of elevating mechanism industry has very important significance.

So far, domestic and international many scholars carry out certain research to the interfacial reaction of melts of titanium alloy and mold material, but research mainly concentrates on the choice and optimization of technological parameter. And Nb content has important effect for the mechanical performance of improving titanium-aluminium alloy especially high-temperature mechanical property. But the relation of its content and interfacial reaction degree in titanium-aluminium alloy, also lacks unified understanding. Therefore the titanium-aluminium alloy that contrasts different N b content by serial experiment interfacial reaction degree under the same conditions, obtains optimum Nb content ratio, has great importance for titanium-aluminium alloy optimizing components from now on.

Summary of the invention

Technical problem: the Ti-Al alloy cast of the different N b content obtaining for directional solidification herein, in the face of its in whole directional solidification process due to problems such as pollution occur for high temperature and casting mold coating material and react, make an appraisal in conjunction with microstructure, Elements Diffusion, thing phase change and the hard corresponding foundry goods interfacial reaction of Degree distributions degree, to finding out best alloying component ratio, and then improve the quality of Ti-Al alloy cast, reduce the cost of subsequent treatment.

For reaching above-mentioned technical problem, the design is achieved through the following technical solutions, and it comprises the steps:

A. adopt the Ti-Al alloy cast of vertical centrifugal type vacuum induction casting furnace founding different N b content. After completing, rapid cooling as cast condition samples, and removes greasy dirt, scale and the oxide skin etc. of specimen surface, and its detailed process as shown in Figure 1;

B. select Al₂O₃As crucible material, Y₂O₃As shell inside coating material, the brushing thickness of coating is about 0.5mm, crucible specification position internal diameter 6.5mm, outer wall 8mm, and the sintering schedule of coating is 950 DEG C × 2h;

C. the alloy bar that cuts diameter 6mm from female ingot middle part electric spark, polishing scale removal, be coated with Y with putting into after acetone cleaning, drying₂O₃The Al of layer₂O₃Shell. Use vacuum induction heating bridgman furnace to carry out directional solidification process,

D. directional solidification parameter reasonable in design, and adopt be rapidly heated, the technique of insulation, rapid cooling combination;

E. adopt the microscopic appearance of sem observation interface, the element distribution analysis at respective interface place adopts energy dispersive spectrometry test. By the thing phase composition on X-ray diffractometer analytical sample surface. Obtain the microhardness of near interface in conjunction with microhardness testers.

By this experimentation, reasonably select directional solidification processes parameter, and according to strict experimental procedure and requirement of experiment, obtain outward appearance and inherent quality density is very high, ganoid foundry goods, has realized the objective evaluation to interfacial reaction degree. According to the composition of foundry goods and size Selection directional solidification temperature and temperature retention time, and mate suitable vacuum. Cutting is afterwards cleaned, and organize accordingly and performance test, and Elements Diffusion and thing phase composition to respective regions detects, and obtains the objective evaluation to interfacial reaction degree.

The determination and analysis of the surface contamination situation in directional solidification to different N b content Ti-Al alloy cast, optimizes preferably Nb content proportioning herein, for corresponding facilitation has been played in the raising of Ti-Al alloy cast quality and the reduction of cost.

Brief description of the drawings

Fig. 1 is interface scanned photograph figure.

Fig. 2 element is at the scatter diagram of interface.

The thing phase composition figure of Fig. 3 interface.

Fig. 4 interface is to the hardness distribution of matrix.

Detailed description of the invention

A kind of method of measuring titanium-aluminium alloy and the casting mold coating interface extent of reaction.

(1) female ingot casting, experimental raw is respectively sponge Ti, Al powder, Cr powder, AlV and AlNb particle (granular 325 orders), and proportion scale is chosen by the parameter of component portion, and the final proportioning obtaining is in table 1. Experiment adopts vertical centrifugal type vacuum induction casting furnace to carry out founding, and in stove, vacuum keep passes into the protection of Ar gas behind 0.5Pa left and right, repeatedly keeps vacuum at 0.08Pa left and right, pressure release rate < 0.1Pa/mm after three times. After fusion cast process, ingot casting back-off is put into founding again, repeatedly make for three times ingot casting element be evenly distributed, get an inspection component distributing. Reach ingot casting after the requirement female ingot as directional solidification;

(2) reach the standard grade and cut the alloy bar of middle part diameter 6mm from above-mentioned alloy pig, grind off skim-coat oxide skin, with for subsequent use at 120 DEG C of oven dry 1h after acetone ultrasonic cleaning;

(3) select Al₂O₃As crucible material, Y₂O₃As shell inside coating material, the brushing thickness of coating is about 0.5mm, crucible specification position internal diameter 6mm, outer wall 10mm, and the sintering schedule of coating is 950 DEG C × 2h;

(4) casting mold is carried out to heat stepwise, first paragraph is room temperature to 1300 DEG C, heat time 3h, and second segment is 1300 DEG C of temperature to setting. The technological parameter such as heating-up temperature and temperature retention time is in table 3. Pull length is 100mm. Cooling procedure selects gallium indium liquid metal as cooling fluid. Powered-down afterwards, sample cools to room temperature with the furnace and takes out;

(5) then sample is ground, after polishing, on HVS-50 digital display microhardness instrument, carry out vickers microhardness test, test specification is to change from interface to alloy substrate. Interval with minimum 5um under the load of 5N is measured, and the load time is 15s, and each position measurement is averaged for 3 times, determines thus interfacial reaction layer thickness. The element distribution analysis at sample interface place adopts German Brooker Quantax400-10 type energy dispersive spectrometry; The material phase analysis of specimen surface adopts German Brooker D8AdanceX x ray diffractometer x, and its test condition is voltage 40kV, electric current 30mA, and plate target material is Cu target. Tissue topography's observation analysis of foundry goods conversion zone and foundry goods matrix adopts U.S. FEIQuantaTM250 type SEM;

Sample testing result is as follows:

Scan test: interfacial reaction region has been carried out to the scanning of different multiples and position, obtained corresponding microscopic appearance. As shown in Figure 1. There is obvious line of demarcation on surface with matrix, and coarse part can be regarded boundary layer as.

Element distributes and tests: outside ESEM, then the element of corresponding site is distributed and added up, the region of constituent content sudden change is exactly the marginal part of conversion zone in scanned photograph, as shown in Figure 2.

The thing experiment that distributes mutually: interface has further been done thing and tested mutually, to distribute and to determine the thing phase composition of respective regions in conjunction with element. Result as shown in Figure 3.

Hardness distributes and tests: on above-mentioned experiment basis, carry out the hardness distribution experiment from interface to matrix, thereby confirm corresponding interfacial layer thickness, determine more intuitively the degree of interfacial reaction. Result as shown in Figure 4.

Finally can analyze and draw: the increase of Nb content in titanium-aluminium alloy can improve alloy high-temp activity, cause the increasing of interfacial reaction degree, therefore keeping under the stable prerequisite of alloy property, the addition that reduces Nb content can reduce interfacial reaction degree, improves the quality of foundry goods as far as possible.

For those skilled in the art person, all to the design make simple modification, be equal to replace with improve, all should be within the design's protection domain.

Claims (6)

1. reduce directionally solidifying titanium aluminum alloy foundry goods and the alloy design method that casting mold coating interface reacts, it is characterized in that comprising the steps:

A. keep technological parameter constant, by alloy designs, add respectively the Nb element of different content in female ingot, female ingot is refined by vertical centrifugal vacuum induction casting furnace, and after completing, rapid cooling as cast condition samples, and removes greasy dirt, scale and the oxide skin etc. of specimen surface;

B. select Al₂O₃As crucible material, Y₂O₃As shell inside coating material, the brushing thickness of coating is about 0.5mm, crucible specification position internal diameter 6.5mm, outer wall 8mm, and the sintering schedule of coating is 950 DEG C × 2h;

C. the alloy bar that cuts diameter 6mm from female ingot middle part electric spark, polishing scale removal, be coated with Y with putting into after acetone cleaning, drying₂O₃The Al of layer₂O₃Shell; Use vacuum induction heating bridgman furnace to carry out directional solidification process;

D. select rational directional solidification parameter, and adopt be rapidly heated, the technique of insulation, rapid cooling combination;

E. on HVS-50 digital display microhardness instrument, carry out vickers microhardness test, test specification is to change from interface to alloy substrate; Interval with minimum 5um under the load of 5N is measured, and the load time is 15s, and each position measurement is averaged for 3 times, determines thus interfacial reaction layer thickness; The element distribution analysis at sample interface place adopts German Brooker Quantax400-10 type energy dispersive spectrometry; The material phase analysis of specimen surface adopts German Brooker D8AdanceX x ray diffractometer x, and its test condition is voltage 40kV, electric current 30mA, and plate target material is Cu target; Tissue topography's observation analysis of foundry goods conversion zone and foundry goods matrix adopts U.S. FEIQuantaTM250 type SEM.

2. casting technique as claimed in claim 1, is characterized in that: female ingot is refined by vertical centrifugal vacuum induction casting furnace, and after completing, rapid cooling as cast condition samples, and removes greasy dirt, scale and the oxide skin etc. of specimen surface, and table 1 is titanium-aluminium alloy composition.

3. coating manufacturing process as claimed in claim 1, is characterized in that: select Al₂O₃As crucible material, Y₂O₃As shell inside coating material, the brushing thickness of coating is about 0.5mm, crucible specification position internal diameter 6.5mm, outer wall 8mm, the sintering schedule of coating is 950 DEG C × 2h, concrete composition is as shown in table 2, and the painting slip pH value configuring should be between 9-10, and viscosity is at 0.45-0.55Pas.

4. technique as claimed in claim 1, is characterized in that: cut the alloy bar of diameter 6mm from female ingot middle part electric spark, polishing scale removal, be coated with Y with putting into after acetone cleaning, drying₂O₃The Al of layer₂O₃Shell; Use vacuum induction heating bridgman furnace to carry out directional solidification process.

5. technique as claimed in claim 1, directional solidification parameter reasonable in design, and adopt be rapidly heated, the technique of insulation, rapid cooling combination, concrete technological parameter is as shown in table 3.

6. technique as claimed in claim 1, the microscopic appearance of employing sem observation interface, the element distribution analysis at respective interface place adopts energy dispersive spectrometry test; By the thing phase composition on X-ray diffractometer analytical sample surface; Obtain the microhardness of near interface in conjunction with microhardness testers; And then whole interfacial reaction is evaluated.