CN114178527B - A powder metallurgy preparation method of variable texture titanium material - Google Patents

Abstract

The invention discloses a powder metallurgy preparation method of a variable texture titanium material, which comprises: preheating high-pressure preformed pure titanium or titanium alloy to a temperature above its β transformation point, and keeping it warm, and simultaneously preheating an extrusion cylinder and an extrusion die; wherein, elements added to the titanium alloy must not expand the α+β two-phase region of the titanium alloy; rapidly transferring the preheated pure titanium or titanium alloy billet to the preheated hot extrusion cylinder, and performing hot extrusion, so that the billet passes through the hot extrusion die hole; wherein, the hot extrusion process needs to pass through the pure titanium Or complete within the period of time before and after the phase transition point of the titanium alloy billet. The obtained titanium rod can be divided into two parts as a whole, that is, the extruded part whose material temperature is above the β-transition temperature and the extruded part whose material temperature is lowered below the β-transition temperature. The two parts have different material textures. The titanium material prepared by the invention has a continuous structure but changes in texture, each part can bear different loads, and can adapt to variable loads, and the preparation method is simple and easy to popularize.

Description

A powder metallurgy preparation method of variable texture titanium material

technical field

The invention belongs to the technical field of metal material processing, and in particular relates to a powder metallurgy preparation method of variable texture titanium material.

Background technique

As a high-strength lightweight metal, titanium metal has good corrosion resistance and high strength. Therefore, it is widely used in aerospace, medical and health fields.

In the field of aerospace, high-strength titanium alloys are often used as lightweight materials to reduce the weight of aircraft. The strength of high-strength titanium alloys used as structural materials can reach 800-1200MPa, or even higher.

In the field of medical and health care, titanium and titanium alloys are often implanted in the human body to replace or assist severely damaged tissue structures in the human body, such as bones, joints, heart valves, and bone fixation clips. Metal titanium is non-toxic, and it is not easy to react with human tissues after being implanted in the human body. It is not easy to be corroded by human body fluids and tissue fluids, has no harm to the human body, and is well combined with human tissues, with good biocompatibility. Therefore, titanium metal is regarded as one of the "biophilic metals", and it is also one of the three major metal materials widely used in biomedicine.

Due to the wide application of titanium and titanium alloys, correspondingly, the preparation, processing and forming technology and microstructure regulation of titanium and titanium alloys have also attracted extensive attention of researchers.

According to the microstructure classification, titanium and titanium alloys can be divided into α titanium, β titanium and α+β titanium. In the equilibrium state, when the temperature is lower than 882°C, titanium presents as α-titanium with close-packed hexagonal structure; when it is higher than 882°C, titanium presents as β-titanium with body-centered cubic structure; by adding alloying elements and proper heat treatment, α+β-titanium with two-phase coexistence can be obtained. Among them, α-titanium has the most stable structure, better plasticity, and slightly lower strength; β-titanium can show higher strength without heat treatment, and can be further strengthened after aging treatment, and the strength at room temperature can reach more than 1300MPa; α+β titanium has a dual-phase structure, good structure stability, and good toughness. Compared with the annealed state, the strength after heat treatment can be increased by more than 50%.

Among the three types of titanium, α-titanium and α+β-titanium are used most frequently. The α+β titanium alloy contains α-stable elements or β-stable elements, such as aluminum and vanadium. If titanium alloys are implanted into the human body, these elements will easily diffuse into the surrounding human tissues and cause harm to the human body (I. er Sci Eng C Mater Biol Appl 60 (2016) 230-238.). To solve this problem, there are roughly two solutions. The first is to develop new titanium alloys and use elements that are harmless to the human body as phase stabilizing elements; the second is to use pure titanium as an implant material.

In addition, titanium alloy has high strength and large elastic modulus, which is very suitable for application in the aerospace industry. However, the strength of titanium alloy is quite different from that of human bones, and there may be a problem of strength mismatch between the two. At the joints of the human body, the load situation is more complicated. The loads on different positions of the same joint may be different, and the loads on the joints before and after deformation may also be different. In aerospace vehicles, there are also some moving components that are subjected to different loads or variable loads. If there are different tissues in different locations in the same continuous material, then different locations will have different load-bearing capabilities, which has a better match with the forces of human tissues and moving components of aerospace vehicles. The existing preparation processes such as casting, plastic deformation and heat treatment of titanium and titanium alloys are dedicated to obtaining materials with uniform structure, and there is no report on the research of double texture in the same continuous material.

Contents of the invention

The α+β two-phase region in pure titanium is very narrow, almost negligible. The temperature of pure titanium is raised above the β transformation point, and then it is thermally processed. The material experiences heat loss during thermal processing, and crosses the phase transition point. The materials extruded before and after crossing the phase transition point can obtain different textures.

Neutral elements in titanium alloys can be infinitely solid-soluble with titanium, and will not expand the α+β two-phase region of titanium alloys, such as zirconium, hafnium, etc. (as shown in Figure 1); although some elements in titanium alloys cannot be infinitely solid-soluble with titanium, when their content is within a certain limit, they will not expand the two-phase region of titanium, such as gallium (atomic ratio is not greater than 15%), tin (atomic ratio is not greater than 15%), etc. (as shown in Figure 1). The titanium alloy containing only the above elements is also processed similarly to pure titanium, and variable texture can also be obtained in the same continuous material.

In order to prepare a titanium material with a continuous structure but a variable structure and adapt to a complex load environment, this application proposes a powder metallurgy preparation method for a variable texture titanium material for pure titanium and titanium alloys that only add elements that will not expand the α+β two-phase region of titanium.

The present invention is specifically achieved through the following technical solutions:

The invention provides a powder metallurgy preparation method of variable texture titanium material, comprising:

Preheating the high-pressure preformed pure titanium or titanium alloy to a temperature above its β transformation point, keeping it warm, and simultaneously preheating the extrusion cylinder and extrusion die; wherein, the elements added to the titanium alloy must not expand the α+β two-phase region of the titanium alloy;

Rapidly transfer the preheated pure titanium or titanium alloy billet into the preheated hot extrusion cylinder, perform hot extrusion, and make the billet pass through the hot extrusion die hole; wherein, the hot extrusion process needs to be completed within a time period before and after crossing the phase transition point of the pure titanium or titanium alloy billet.

As a further description of the present invention, the preheating temperature of the pure titanium or titanium alloy is 900-1500°C.

As a further illustration of the present invention, the preheating temperature of the extrusion barrel and the extrusion die is 300-800°C.

As a further description of the present invention, the extrusion rate during the hot extrusion process is 1-10 mm/s.

As a further description of the present invention, the extrusion ratio in the hot extrusion process is 16:1˜64:1.

As a further description of the present invention, the high-pressure preforming process specifically includes: loading pure titanium powder or titanium alloy powder containing required elemental components into a mold, and forming under high pressure at room temperature; wherein, the required elemental components must not expand the α+β two-phase region of the titanium alloy.

As a further description of the present invention, the pressure of the high-pressure preforming is not lower than 300 MPa, and the holding time is not lower than 1 min.

Compared with the prior art, the present invention has the following beneficial technical effects:

1. Pure titanium does not have a two-phase region, while titanium alloys (only containing elements such as zirconium, hafnium, gallium, and tin) have a narrow two-phase region; the β transition line of titanium alloys (only containing elements such as zirconium, hafnium, gallium, and tin) is very close to the lower boundary of the two-phase region, and has little effect on the β→α phase transition. Preheating pure titanium and titanium alloys above the β transformation point will cool down due to heat loss during extrusion. The part extruded above the β transformation point can obtain β titanium with preferred grain orientation during extrusion. This part crosses the phase transition point during the heat loss process, so cooling below the phase transition point can obtain α titanium with a wide distribution of grain orientation; and the extruded part that is cooled below the β transformation point is already in the α state. Therefore, no phase transition will occur, and the preferred orientation can also be retained. down. Thereby, varying textures can be obtained on the same structurally continuous material.

2. The combination of different extrusion rates, extrusion ratios and preheating temperatures of pure titanium or titanium alloys (only containing elements such as zirconium, hafnium, gallium, and tin) can control the proportion of different structural segments of the obtained extruded materials, and obtain materials that meet different needs.

3. The present invention mainly utilizes pure titanium without two-phase region and titanium alloy with narrow two-phase region (containing only elements such as zirconium, hafnium, gallium and tin), heat loss during hot extrusion process, and grain orientation change of phase transition to obtain variable texture material, and can break through the limitations of other process parameters except material preheating temperature, such as preheating temperature, heating rate, holding time, extrusion rate and extrusion ratio.

4. The method of the present invention is not only applicable to pure titanium, but also applicable to titanium alloys added with elements that do not expand the two-phase region of titanium, so it can also be used to process higher-strength titanium alloys.

Description of drawings

FIG. 1 is a schematic diagram of the influence of elements (such as zirconium, tin, hafnium, gallium, etc.) that do not expand the titanium two-phase region on the titanium two-phase region and the β transition line referenced by the present invention.

Fig. 2 is the segmentation method of the extruded material obtained in Example 1 of the present invention.

Fig. 3(a-e) is the microstructure of different segments in the extruded material obtained by using pure titanium in Example 1 of the present invention.

Fig. 4(a-e) is the microstructure of different segments in the extruded material obtained by using pure titanium in Example 2 of the present invention.

Fig. 5 (a and b) is the microstructure of different segments in the extruded material obtained by using TC4 in Example 3 of the present invention.

FIG. 6 is a schematic diagram of the phase area of TC4 referred to in Embodiment 3 of the present invention.

Detailed ways

In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the case of no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention.

The invention provides a powder metallurgy preparation method of variable texture titanium material, comprising:

Preheating the high-pressure preformed pure titanium or titanium alloy to a temperature above its β transformation point, keeping it warm, and simultaneously preheating the extrusion cylinder and extrusion die; wherein, the elements added to the titanium alloy must not expand the α+β two-phase region of the titanium alloy;

Rapidly transfer the preheated pure titanium or titanium alloy billet into the preheated hot extrusion cylinder, perform hot extrusion, and make the billet pass through the hot extrusion die hole; wherein, the hot extrusion process needs to be completed within a time period before and after crossing the phase transition point of the pure titanium or titanium alloy billet.

Pure titanium does not have a two-phase region, while titanium alloys (containing only elements such as zirconium, hafnium, gallium, and tin) have a narrow two-phase region; the β transition line of titanium alloys (containing only elements such as zirconium, hafnium, gallium, and tin) is very close to the lower boundary of the two-phase region, and has little effect on the β→α phase transition. Preheating pure titanium and titanium alloys above the β transformation point will cool down due to heat loss during extrusion. The part extruded above the β transformation point can obtain β titanium with preferred grain orientation during extrusion. This part crosses the phase transition point during the heat loss process, so cooling below the phase transition point can obtain α titanium with a wide distribution of grain orientation; and the extruded part that is cooled below the β transformation point is already in the α state. Therefore, no phase transition will occur, and the preferred orientation can also be retained. down. Thereby, varying textures can be obtained on the same structurally continuous material.

In a preferred manner, the preheating temperature of the pure titanium or titanium alloy is 900-1500°C.

From the above analysis, it can be seen that the lower limit of the preheating temperature of titanium materials must be higher than the β transformation point of the material (882°C for pure titanium). By combining the preheating temperature of the titanium material with the preheating temperature of the extrusion die and the extrusion rate, variable-textured titanium materials with different lengths can be prepared. If you want to obtain longer randomly oriented grains, the extruded part should be as long as possible when the temperature is higher than the phase transition point. Pure titanium or titanium alloy materials and extrusion dies should use higher preheating temperatures and lower extrusion rates. Therefore, the upper limit of the preheating temperature of pure titanium or titanium alloy materials can approach the melting point (1668°C for pure titanium). Therefore, the preferred preheating temperature of the pure titanium or titanium alloy is 900-1500°C.

In a preferred manner, the preheating temperature of the extrusion cylinder and the extrusion die is 300-800°C.

Since it takes a certain amount of time to complete the extrusion, and the preheating temperature required by the titanium material is very high, it is necessary to control the heat loss rate of the titanium material to control the cooling rate. In order to match the preheating temperature and extrusion rate of the titanium material, if a faster heat loss rate is required, the temperature difference between the titanium material and the extrusion die should be larger, and the extrusion die requires a lower preheating temperature; if a slower heat loss rate is required, the temperature difference between the titanium material and the extrusion die should be small, and the extrusion die requires a higher preheating temperature. Therefore, the preheating temperature of the extrusion cylinder and the extrusion die is preferably 300-800°C.

In a preferred manner, the extrusion rate during the hot extrusion process is 1-10 mm/s; the extrusion ratio during the hot extrusion process is 16:1-64:1.

In the present invention, in order to obtain the variable texture, the process must be controlled to ensure that the titanium material crosses the phase transition point during the extrusion process. The preheating temperature of the titanium material must be higher than the phase transition point, and at the same time cooperate with the appropriate mold preheating temperature to make the titanium material have an appropriate heat loss rate and control the appropriate extrusion rate. The combination of the above three can make the titanium material undergo heat loss while being extruded and just cross the phase transition point in the hot extrusion process, so that the variable texture can be obtained in the continuous material; the combination of the preheating temperature of the titanium material, the preheating temperature of the extrusion die and the extrusion rate can also control the length of the different texture segments prepared. Therefore, after comprehensive consideration, the extrusion rate is preferably 1-10mm/s; the extrusion ratio is 16:1-64:1.

In a preferred manner, the high-pressure preforming process specifically includes: loading pure titanium powder or titanium alloy powder containing required elemental components into a mold, and forming under high pressure at room temperature; wherein, the required elemental components must not expand the α+β two-phase region of the titanium alloy.

Further, the pressure of the high-pressure preforming is not lower than 300 MPa, and the holding time is not lower than 1 min.

The following is a specific description with preferred embodiments.

Example 1

The titanium material used in this embodiment is pure titanium.

Step 1, high-pressure preforming: put pure titanium powder with an equivalent particle size of 20 μm into a mold with a diameter of 42 mm, apply 600 MPa high-pressure pre-forming at room temperature, and hold the pressure for 1 minute.

Step 2, preheating the material and the extrusion die: preheat the preformed pure titanium to 1100°C at a heating rate of 2°C/s, and keep it warm for 5 minutes. At the same time, the extrusion barrel and extrusion die were preheated to 400°C.

Step 3, hot extrusion: quickly transfer the preheated pure titanium billet to the preheated hot extrusion barrel with an inner diameter of 43mm, and extrude the head at a rate of 6mm/s, so that the billet passes through the hot extrusion die hole with an inner diameter of 7mm, and the extrusion ratio is 37:1. The material is then allowed to cool naturally.

The above-mentioned extruded pure titanium is divided into sections as shown in Figure 2, and each section of material is taken to observe its microstructure, and its microstructure is shown in Figure 3. L1-L9 marked in FIG. 3 correspond to those shown in FIG. 2 one by one. Since the preheating temperature of the pure titanium billet reaches 1100°C, it has reached above the β transformation point of titanium, so the first extruded part of the material in hot extrusion is extruded in the β state, accompanied by the preferred orientation of the grains. With natural cooling, this part of the material crosses the beta transformation point and transforms into alpha titanium. During the phase transformation process, the grain orientation changes, only a part of the preferred orientation texture is retained, and the grain morphology changes. Therefore, the α-titanium with random shape and wide grain orientation distribution shown in Figure 3 (a and b) is obtained; while the part that is extruded after cooling below the β transformation point is extruded when it is already in the α state, so the phase transition will not occur again, and the preferred orientation of the grains can also be preserved. Finally, an equiaxed crystal with a strong preferred orientation is obtained, as shown in Figure 3 (c-e).

Example 2

The titanium material used in this embodiment is pure titanium.

Step 1, high-pressure preforming: put pure titanium powder with an equivalent particle size of 45 μm into a mold with a diameter of 30 mm, apply 650 MPa high-pressure pre-forming at room temperature, and hold the pressure for 5 minutes.

Step 2, preheating the material and the extrusion die: preheat the preformed pure titanium to 1000°C at a heating rate of 4°C/s, and keep it warm for 15 minutes. At the same time, the extrusion barrel and extrusion die were preheated to 400°C.

Step 3, hot extrusion: quickly transfer the preheated pure titanium billet to a preheated hot extrusion cylinder with an inner diameter of 30 mm, and press the head at a rate of 3 mm/s to make the billet pass through a hot extrusion die hole with an inner diameter of 7 mm, and the extrusion ratio is 18:1. The material is then allowed to cool naturally.

The above-mentioned extruded pure titanium is divided into sections as shown in Figure 2, and each section of material is taken to observe its microstructure, and its microstructure is shown in Figure 4. L1-L9 identified in FIG. 4 correspond to those shown in FIG. 2 . Since the preheating temperature of the pure titanium billet reaches 1000°C, it has reached above the β transformation point of titanium, so the first extruded part of the material in hot extrusion is extruded in the β state, accompanied by the preferred orientation of the grains. With natural cooling, this part of the material crosses the beta transformation point and transforms into alpha titanium. During the phase transformation process, the grain orientation changes, only a part of the preferred orientation texture is retained, and the grain morphology changes. Therefore, the α-titanium with random shape and wide grain orientation distribution shown in Figure 4 (a and b) is obtained; while the part that is extruded after cooling below the β transformation point is extruded when it is already in the α state, so the phase transition will not occur again, and the preferred orientation of the grains can also be retained. Finally, an equiaxed crystal with a strong preferred orientation is obtained, as shown in Figure 4 (c-e).

Combining Example 1 and Example 2, it can be confirmed that when pure titanium is hot-extruded from above the β transformation point, different textures can be obtained in different parts of the extruded material with the progress of heat loss and the appearance of phase transition.

Example 3

This embodiment is used as the comparative example of embodiment 1.

The titanium powder used in this comparative example is TC4 (Ti-6Al-4V) powder with an equivalent particle size of 20 μm; other process parameters used are the same as in Example 1. The obtained extruded rods were sampled according to the segmentation method shown in Figure 2, and their microstructure was characterized, and the microstructure is shown in Figure 5. L1 and L9 identified in FIG. 5 correspond to those shown in FIG. 2 .

TC4 contains both α-stable elements and β-stable elements, and its α+β two-phase region has a large temperature range, as shown in Figure 6. The β transition temperature of TC4 is 995°C. When it is transferred from the preheating furnace to the extrusion die, its temperature has dropped to the α+β dual-phase region due to heat loss; during the entire extrusion process, TC4 is always in the temperature range of the α+β dual-phase region. Since the entire extruded rod is in the same phase region during the whole process of extrusion, when TC4 finally drops to room temperature, the obtained texture is also the same, as shown in Figure 5.

Comparing Example 1 and Example 3, it can be confirmed that in the titanium alloy added with α-stable elements or β-stable elements, since the same continuous material is always in the same phase region during the hot extrusion process, the final texture is the same, and no variable texture material can be obtained.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims (5)

1. A method for preparing a textured titanium material by powder metallurgy, comprising the steps of:

preheating high-pressure preformed pure titanium or titanium alloy to a temperature above the beta transition point of the high-pressure preformed pure titanium or titanium alloy, preserving heat, and simultaneously preheating an extrusion cylinder and an extrusion die; the element added in the titanium alloy is required to not expand an alpha+beta two-phase region of titanium, and the preheating temperature of the pure titanium or the titanium alloy is 900-1500 ℃;

the high-pressure preforming process specifically comprises the following steps: filling pure titanium powder or titanium alloy powder containing required element components into a mould, and forming at room temperature under high pressure; wherein the required element components are required to not expand the alpha+beta two-phase region of titanium;

rapidly transferring the preheated pure titanium or titanium alloy blank into a preheated hot extrusion cylinder for hot extrusion, and enabling the blank to pass through a hot extrusion die hole; wherein the hot extrusion process needs to be completed in a time period before and after crossing the transformation point of the pure titanium or titanium alloy billet.

2. The method of claim 1, wherein the preheating temperature of the extrusion barrel and the extrusion die is 300-800 ℃.

3. The method for preparing the textured titanium material by powder metallurgy according to claim 1, wherein the extrusion rate in the hot extrusion process is 1-10 mm/s.

4. The method for preparing a textured titanium material according to claim 1, wherein the extrusion ratio in the hot extrusion process is 16:1 to 64:1.

5. The method for producing a textured titanium material according to claim 1, wherein the pressure of the high-pressure preform is not lower than 300MPa and the dwell time is not lower than 1min.