A method for preparing an isotropic arc additively manufactured titanium alloy with fine equiaxed β grains

Abstract

The invention discloses a preparation method of an isotropic arc additive manufacturing titanium alloy with fine equiaxed β grains, the method comprising: 1. selecting titanium alloy wire as a matrix alloy, selecting Cu powder, Co powder and Si powder as additives; 2. ball milling and mixing the Cu powder, Co powder and Si powder to obtain a mixed powder; 3. simultaneously feeding the titanium alloy wire and the mixed powder into a molten pool for arc additive manufacturing. The invention promotes the nucleation of a large number of β equiaxed crystals by using β fast eutectoid element Cu, β slow eutectoid element Co and trace element Si to co-segregate at the front of the solid-liquid interface of the arc additive manufacturing titanium alloy molten pool, and limits the growth of β grains during the arc additive manufacturing reheating cycle by rapidly solidifying Ti5Si3, thereby obtaining a titanium alloy with fine equiaxed β grains and almost isotropic. The process is easy to implement, low in cost, wide in application range, short in time, and suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of metal additive manufacturing, and in particular to a method for preparing an isotropic arc additively manufactured titanium alloy with fine equiaxed β grains. Background Art

[0002] With the rapid development of aviation, aerospace and navigation industries, strategic equipment such as launch vehicles, manned spacecraft, aircraft engines and aircraft carriers are developing in the direction of large, lightweight, complex and integrated structure and function, which poses more stringent challenges to traditional manufacturing processes. Additive manufacturing, especially arc additive manufacturing, has gradually gained attention due to its advantages of low cost, high forming efficiency and suitability for manufacturing large-size components. It is called a low-energy, sustainable and green environmentally friendly manufacturing technology by the European Space Agency. Titanium alloys are widely used in aviation, aerospace and navigation due to their high specific strength, good corrosion resistance and non-magnetic properties. However, due to the high temperature gradient inside the molten pool and the characteristics of rapid cooling and heating during arc additive manufacturing, the structure of titanium alloy presents millimeter-scale epitaxial growth of coarse β columnar crystals, resulting in significant anisotropy of mechanical properties of the components.

[0003] At present, researchers mainly focus on increasing the composition supercooling at the front of the solid-liquid interface of the molten pool by regulating process parameters or adding a single alloy element, and promoting the transformation of columnar crystals to equiaxed crystals by increasing the nucleation rate, thereby increasing the volume fraction of equiaxed crystals and even obtaining a fully equiaxed crystal structure. However, the process window for regulating the nucleation rate by process parameters is relatively narrow, and a large amount of a single alloy element is required to promote nucleation in order to achieve sufficient composition supercooling. However, such a large amount of a single alloy element addition will lead to brittle fracture of the alloy. For example, in the arc additive manufacturing of Ti6Al4V titanium alloy, the addition of Ni is as high as 7.5wt.% to obtain a fully equiaxed β crystal structure, and its elongation is only 1% at this time (patent with publication number CN117483786A). Therefore, it is urgent to develop a new preparation method to obtain an isotropic arc additive manufacturing titanium alloy with fine fully equiaxed β grains. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing an isotropic arc additively manufactured titanium alloy with fine equiaxed β grains in view of the deficiencies of the above-mentioned prior art. The method adopts β fast eutectoid element Cu, β slow eutectoid element Co and trace element Si as additives to promote the large-scale nucleation of β equiaxed crystals and limit the growth of β grains, thereby obtaining a titanium alloy with fine equiaxed β grains and almost isotropy, and improving the strength of the titanium alloy, solving the mechanical property anisotropy caused by the coarse β columnar crystals of arc additively manufactured titanium alloys, and the limitations of regulating the β grain morphology and mechanical properties by adjusting process parameters or adding a single alloying element.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an isotropic arc additively manufactured titanium alloy with fine equiaxed β grains, characterized in that the method comprises the following steps:

[0006] Step 1: Material selection: titanium alloy wire is selected as the base alloy, and Cu powder, Co powder and Si powder are selected as additives;

[0007] Step 2, powder mixing: put the Cu powder, Co powder and Si powder selected in step 1 into a ball mill jar, and place it in a ball mill for ball milling and mixing to obtain a mixed powder;

[0008] Step 3. Additive manufacturing: Utilize the wire-powder co-feeding mechanism of the arc additive manufacturing equipment to simultaneously feed the titanium alloy wire selected in step 1 and the mixed powder prepared in step 2 into the molten pool for arc additive manufacturing, realize in-situ alloying, and obtain arc additively manufactured titanium alloy with fine equiaxed β grains; the size of the fine equiaxed β grains is less than 500 μm, and the anisotropy of the tensile strength and elongation after fracture of the arc additively manufactured titanium alloy is less than 1% and 5%, respectively.

[0009] The present invention selects titanium alloy wire as a matrix alloy, and uses Cu powder, Co powder and Si powder as additives. The mixed powder is first prepared by ball milling, and then the titanium alloy wire and the mixed powder are simultaneously fed into a molten pool by a wire-powder co-feeding mechanism of arc additive manufacturing. The composition supercooling caused by the co-segregation of β-fast eutectoid element Cu, β-slow eutectoid element Co and trace element Si at the front edge of the solid-liquid interface of the titanium alloy molten pool manufactured by arc additive manufacturing promotes the massive nucleation of β-equiaxed crystals. The Ti5Si3 formed by rapid solidification limits the growth of β grains during the reheating cycle of arc additive manufacturing, thereby obtaining a titanium alloy with fine equiaxed β grains.

[0010] Normalized growth restriction factor Q n The size of represents the contribution of alloying elements to the supercooling development rate of the frontal components of the solid-liquid interface. Cu and Si have a larger Q n β-fast eutectoid element, Co has the largest Q nThe composite addition of β-slow eutectoid elements, β-fast eutectoid elements and β-slow eutectoid elements can achieve a better composition supercooling effect with a small amount of addition, significantly increase the nucleation rate of β grains, and thus obtain a fully equiaxed β-crystalline structure. In addition, Ti5Si3 can also limit the migration of β grain boundaries, refine β-equiaxed grains, and reduce the β grain size of arc additively manufactured titanium alloys from mm level to μm level. The combined effect of the two ensures the acquisition of fine fully equiaxed β grains, and the fine fully equiaxed β grains play a role in grain refinement strengthening, and Ti5Si3 plays a role in second phase strengthening. Ultimately, with the elongation basically unchanged, the strength of arc additively manufactured titanium alloys is significantly improved, and the isotropy of the mechanical properties of arc additively manufactured titanium alloys is achieved.

[0011] The above-mentioned method for preparing an isotropic arc additively manufactured titanium alloy with fine equiaxed β grains is characterized in that the titanium alloy wire in step one is a near-α titanium alloy, an α+β two-phase titanium alloy or a β titanium alloy.

[0012] The above-mentioned method for preparing an isotropic arc additively manufactured titanium alloy with fine equiaxed β grains is characterized in that the masses of the Cu powder, Co powder and Si powder in step 2 account for 1% to 5%, 1% to 5% and 0.2% to 0.6% of the total mass of the mixed powder and the titanium alloy wire in step 3, respectively.

[0013] The above-mentioned method for preparing an isotropic arc additively manufactured titanium alloy with fine equiaxed β grains is characterized in that the rotation speed of the ball milling mixing in step 2 is 180 rpm, the ball-to-material ratio is 5:1, and the ball milling time is 3 hours.

[0014] The above-mentioned method for preparing an isotropic arc additively manufactured titanium alloy with fine equiaxed β grains is characterized in that the wire feeding speed of the titanium alloy wire in step three is 1200mm / min~3000mm / min, and the powder feeding speed of the mixed powder is 6g / min~15g / min.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. The present invention adopts Cu powder, Co powder and Si powder as additives, and promotes the massive nucleation of β equiaxed crystals through the co-segregation of β fast eutectoid element Cu, β slow eutectoid element Co and trace element Si at the solid-liquid interface front of the arc additively manufactured titanium alloy molten pool, and limits the growth of β grains during the arc additive manufacturing reheating cycle through Ti5Si3 formed by rapid solidification, thereby obtaining a titanium alloy with fine equiaxed β grains and almost isotropy, which significantly improves the strength of the arc additively manufactured titanium alloy while keeping the elongation basically unchanged.

[0017] 2. The present invention achieves a better composition supercooling effect with a small amount of addition by composite addition of β fast eutectoid element Cu and β slow eutectoid element Co, significantly increases the nucleation rate of β grains, thereby ensuring that a fully equiaxed β crystal structure is obtained.

[0018] 3. The Si powder added in the present invention forms Ti5Si3 in the arc additively manufactured titanium alloy, which limits the growth of β grains during the arc additively manufactured reheat cycle, refines the equiaxed β crystals, and reduces the β grain size of the arc additively manufactured titanium alloy from mm level to μm level, thereby obtaining a titanium alloy with fine equiaxed β grains.

[0019] 4. The isotropic arc additively manufactured titanium alloy with fine equiaxed β grains prepared by the present invention has excellent mechanical properties, and the anisotropy of its tensile strength and elongation after fracture is less than 1% and 5% respectively, ultimately achieving isotropy of mechanical properties.

[0020] 5. The Cu powder, Co powder and Si powder selected in the present invention can be prepared by the most common mass production method - atomization method, and they have wide sources, low costs and easy to obtain raw materials.

[0021] 6. The preparation process of the present invention is easy to implement, low in cost, has a wide range of applications, and the entire preparation process is short in time, which is suitable for industrial mass production. It also provides new ideas for the design of new arc additive manufacturing titanium alloys.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a physical picture of the TA15 titanium alloy wire used in Example 1 of the present invention.

[0024] Figure 2 The morphology diagram of Cu powder, Co powder and Si powder used in Example 1 of the present invention.

[0025] Figure 3 This is the microstructure diagram of the arc additively manufactured TA15-5Cu-1Co-0.2Si alloy prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] Example 1

[0027] This embodiment includes the following steps:

[0028] Step 1: Material selection: Figure 1 The TA15 titanium alloy wire (close to α titanium alloy) with a diameter of φ1.6 mm shown in the figure is the base alloy. Figure 2The atomized spherical Cu powder and Co powder with a particle size of 46 μm to 150 μm and irregular Si powder with a particle size of 200 nm are shown as additives;

[0029] Step 2, powder mixing: put the Cu powder, Co powder and Si powder selected in step 1 into a ball mill jar, and place it in a ball mill for ball milling and mixing, the ball milling speed is 180rpm, the ball-to-material ratio is 5:1, and the ball milling time is 3h to obtain a mixed powder; the mass of the Cu powder, Co powder and Si powder accounts for 5%, 1% and 0.2% of the total mass of the mixed powder and the titanium alloy wire in step 3, respectively;

[0030] Step 3, additive manufacturing: using the wire-powder co-feeding mechanism of the arc additive manufacturing equipment, the TA15 titanium alloy wire selected in step 1 and the mixed powder prepared in step 2 are simultaneously fed into the molten pool at a wire feeding speed of 2400 mm / min and a powder feeding speed of 10 g / min for arc additive manufacturing to achieve in-situ alloying. The process parameters of the arc additive manufacturing are: voltage 12 V, current 120 A, welding speed 350 mm / min, and an arc additively manufactured TA15-5Cu-1Co-0.2Si alloy with fine equiaxed β grains of about 324 μm in size is obtained, such as Figure 3 shown.

[0031] After testing, the yield strengths of the transverse and longitudinal tensile specimens of the arc additively manufactured TA15-5Cu-1Co-0.2Si alloy prepared in this embodiment were 1060 MPa and 1034 MPa, respectively, the tensile strengths were 1164 MPa and 1157 MPa, respectively, the elongations after fracture were 8.8% and 9.1%, respectively, and the anisotropy indexes of the tensile strength and the elongation after fracture were 0.6% and 3.3%, respectively.

[0032] Example 2

[0033] The difference between this embodiment and embodiment 1 is that the masses of the Cu powder, Co powder and Si powder in step 2 account for 1%, 5% and 0.6% of the total mass of the mixed powder and titanium alloy wire in step 3, respectively; and an arc additively manufactured TA15-1Cu-5Co-0.6Si alloy with fine equiaxed β grains with a size of about 300 μm is obtained.

[0034] After testing, the yield strengths of the transverse and longitudinal tensile specimens of the arc additively manufactured TA15-1Cu-5Co-0.6Si alloy prepared in this embodiment were 952 MPa and 916 MPa, respectively, the tensile strengths were 1024 MPa and 1017 MPa, respectively, the elongations after fracture were 10.4% and 10.7%, respectively, and the anisotropy indexes of the tensile strength and the elongation after fracture were 0.7% and 2.8%, respectively.

[0035] Comparative Example 1

[0036] This comparative example comprises the following steps:

[0037] Step 1: Material selection: Select TA15 titanium alloy wire with a diameter of φ1.6mm;

[0038] Step 2. Additive manufacturing: Using the wire-powder feeding mechanism of the arc additive manufacturing equipment, the TA15 titanium alloy wire selected in step 1 is fed into the molten pool at a wire feeding speed of 2400 mm / min for arc additive manufacturing. The process parameters of arc additive manufacturing are: voltage 12 V, current 120 A, welding speed 350 mm / min, and arc additive manufacturing TA15 titanium alloy with coarse columnar β grains with a size of about 3.5 mm is obtained.

[0039] After testing, the yield strengths of the transverse and longitudinal tensile specimens of the arc additively manufactured TA15 titanium alloy prepared in this comparative example were 879 MPa and 821 MPa respectively, the tensile strengths were 976 MPa and 954 MPa respectively, the elongations after fracture were 6.7% and 11.8% respectively, and the anisotropy indexes of the tensile strength and the elongation after fracture were 2.3% and 43.2% respectively.

[0040] By comparing Example 1 of the present invention with Comparative Example 1, it can be seen that the present invention transforms the β grains of the arc additively manufactured TA15 titanium alloy from columnar crystals to fully equiaxed crystal structures by adding a mixed powder of Cu powder, Co powder and Si powder, and the β grain size is reduced by about 90.7%; at the same time, the arc additively manufactured alloy prepared by introducing fine fully equiaxed β grains has excellent mechanical properties, and the anisotropy of its tensile strength and elongation after fracture is reduced by about 73.9% and 92.4%, respectively, reaching 0.6% and 3.3%, respectively. It is a high-strength, high-plasticity, isotropic arc additively manufactured titanium alloy.

[0041] Example 3

[0042] The difference between this embodiment and Embodiment 1 is that: in step 1, TC4 titanium alloy wire (α+β two-phase titanium alloy) with a diameter of φ1.2 mm is selected as the base alloy; the masses of the Cu powder, Co powder and Si powder in step 2 account for 1.5%, 4% and 0.5% of the total mass of the mixed powder and titanium alloy wire in step 3, respectively; the TC4 titanium alloy wire and the mixed powder in step 3 are respectively fed into the molten pool at a wire feeding speed of 1200 mm / min and a powder feeding speed of 6 g / min for arc additive manufacturing, and the process parameters of the arc additive manufacturing are: voltage 12 V, current 110 A, welding speed 300 mm / min, and an arc additively manufactured TC4-1.5Cu-4Co-0.5Si alloy with fine equiaxed β grains with a size of about 365 μm is obtained.

[0043] After testing, the yield strengths of the transverse and longitudinal tensile specimens of the arc additively manufactured TC4-1.5Cu-4Co-0.5Si alloy prepared in this embodiment were 929 MPa and 891 MPa, respectively, the tensile strengths were 1005 MPa and 997 MPa, respectively, the elongations after fracture were 13.8% and 14.3%, respectively, and the anisotropy indexes of the tensile strength and the elongation after fracture were 0.8% and 3.5%, respectively.

[0044] Comparative Example 2

[0045] The difference between this comparative example and Example 3 is that Cu powder, Co powder and Si powder are not selected, and TC4 titanium alloy wire with a diameter of φ1.2 mm is directly fed into the molten pool at a wire feeding speed of 2400 mm / min for arc additive manufacturing, thereby obtaining arc additively manufactured TC4 titanium alloy with coarse columnar β grains with a size of about 3.8 mm.

[0046] After testing, the yield strengths of the transverse and longitudinal tensile specimens of the arc additively manufactured TC4 titanium alloy prepared in this comparative example were 752 MPa and 701 MPa respectively, the tensile strengths were 823 MPa and 799 MPa respectively, the elongations after fracture were 9.3% and 15.6% respectively, and the anisotropy indexes of the tensile strength and the elongation after fracture were 2.9% and 40.4% respectively.

[0047] By comparing Example 3 of the present invention with Comparative Example 2, it can be seen that the present invention transforms the β grains of the arc additively manufactured TC4 titanium alloy from columnar crystals to fully equiaxed crystal structures by adding a mixed powder of Cu powder, Co powder and Si powder, and the β grain size is reduced by about 90.4%; at the same time, the arc additively manufactured TC4-1.5Cu-4Co-0.5Si alloy prepared by introducing fine fully equiaxed β grains has excellent mechanical properties, and the anisotropy of its tensile strength and elongation after fracture are reduced by about 72.4% and 91.3%, respectively, reaching 0.8% and 3.5%, respectively. It is a high-strength, high-plasticity, isotropic arc additively manufactured titanium alloy.

[0048] Example 4

[0049] The difference between this embodiment and Embodiment 1 is that: in step one, a TB6 titanium alloy wire (β titanium alloy) with a diameter of φ2.0 mm is selected as the base alloy; the masses of the Cu powder, Co powder and Si powder in step two account for 2.5%, 2% and 0.4% of the total mass of the mixed powder and the titanium alloy wire in step three, respectively; in step three, the TB6 titanium alloy wire and the mixed powder are simultaneously fed into the molten pool at a wire feeding speed of 3000 mm / min and a powder feeding speed of 15 g / min for arc additive manufacturing, and the process parameters of the arc additive manufacturing are: voltage 14 V, current 140 A, welding speed 750 mm / min, and an arc additively manufactured TB6-2.5Cu-2Co-0.4Si alloy with fine equiaxed β grains with a size of about 283 μm is obtained.

[0050] After testing, the yield strengths of the transverse and longitudinal tensile specimens of the arc additively manufactured TB6-2.5Cu-2Co-0.4Si alloy prepared in this embodiment were 1213 MPa and 1164 MPa, respectively, the tensile strengths were 1284 MPa and 1272 MPa, respectively, the elongations after fracture were 7.5% and 7.7%, respectively, and the anisotropy indexes of the tensile strength and the elongation after fracture were 0.9% and 2.6%, respectively.

[0051] Comparative Example 3

[0052] The difference between this comparative example and Example 4 is that Cu powder, Co powder and Si powder are not selected, and TB6 titanium alloy wire with a diameter of φ2.0 mm is directly fed into the molten pool at a wire feeding speed of 3000 mm / min for arc additive manufacturing, thereby obtaining arc additively manufactured TB6 titanium alloy with coarse columnar β grains with a size of about 3 mm.

[0053] After testing, the yield strengths of the transverse and longitudinal tensile specimens of the arc additively manufactured TB6 titanium alloy prepared in this comparative example were 1036 MPa and 974 MPa respectively, the tensile strengths were 1112 MPa and 1064 MPa respectively, the elongations after fracture were 5.2% and 8.4% respectively, and the anisotropy indexes of the tensile strength and the elongation after fracture were 4.3% and 38.1% respectively.

[0054] By comparing Example 4 of the present invention with Comparative Example 3, it can be seen that the present invention transforms the β grains of the arc additively manufactured TB6 titanium alloy from columnar crystals to fully equiaxed crystal structures by adding a mixed powder of Cu powder, Co powder and Si powder, and the β grain size is reduced by about 90.6%; at the same time, the TB6-2.5Cu-2Co-0.4Si alloy prepared by introducing fine fully equiaxed β grains has excellent mechanical properties, and its anisotropy of tensile strength and elongation after fracture is reduced by about 79.1% and 93.2%, respectively, reaching 0.9% and 2.6%, respectively. It is a high-strength, high-plasticity, isotropic arc additively manufactured titanium alloy.

[0055] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an isotropic arc additively manufactured titanium alloy having fine equiaxed β grains, characterized in that: The method comprises the following steps: Step 1: Material selection: titanium alloy wire is selected as the base alloy, and Cu powder, Co powder and Si powder are selected as additives; Step 2, powder mixing: put the Cu powder, Co powder and Si powder selected in step 1 into a ball mill jar, and place it in a ball mill for ball milling and mixing to obtain a mixed powder; Step 3, additive manufacturing: using the wire-powder co-feeding mechanism of the arc additive manufacturing equipment, the titanium alloy wire selected in step 1 and the mixed powder prepared in step 2 are simultaneously fed into the molten pool for arc additive manufacturing, so as to realize in-situ alloying and obtain arc additively manufactured titanium alloy with fine equiaxed β grains; the size of the fine equiaxed β grains is less than 500 μm, and the anisotropy of the tensile strength and elongation after fracture of the arc additively manufactured titanium alloy is less than 1% and 5%, respectively; The masses of the Cu powder, Co powder and Si powder in step 2 account for 1% to 5%, 1% to 5% and 0.2% to 0.6% of the total mass of the mixed powder and the titanium alloy wire in step 3, respectively.

2. The method for preparing an isotropic arc additively manufactured titanium alloy having fine equiaxed β grains according to claim 1, characterized in that: The titanium alloy wire material described in step 1 is a near-α titanium alloy, an α+β two-phase titanium alloy or a β titanium alloy.

3. The method for preparing an isotropic arc additively manufactured titanium alloy having fine equiaxed β grains according to claim 1, characterized in that: The ball milling mixing speed in step 2 is 180 rpm, the ball-to-material ratio is 5:1, and the ball milling time is 3 h.

4. The method for preparing an isotropic arc additively manufactured titanium alloy having fine equiaxed β grains according to claim 1, characterized in that: The wire feeding speed of the titanium alloy wire in step 3 is 1200 mm / min~3000 mm / min, and the powder feeding speed of the mixed powder is 6 g / min~15 g / min.

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