JP4517088B2 - Method to improve ductility and strength of lightweight heat-resistant intermetallic compound by adding third element particles - Google Patents

Description

  The present invention relates to a method for improving the ductility and strength of a lightweight heat-resistant intermetallic compound. More specifically, the present invention relates to a method for improving the ductility and strength of a lightweight heat-resistant intermetallic compound by adding chromium as a third element.

  Conventionally, a method of adding a third element in a molten state has been studied for improving characteristics such as high-temperature strength of intermetallic compounds, particularly NiAl and TiAl. However, in this method, addition in a trace amount that does not affect the basic structure of the metal structure is the limit, and therefore a remarkable effect due to the addition of the third element could not be expected. In addition, since the added molten material is hard and brittle, the metal structure cannot be refined by forging or the like, and a material with excellent mechanical properties and a uniform metal structure cannot be obtained. NiAl or TiAl intermetallic compounds are low-radiation, corrosion-resistant, high-melting-point, lightweight materials, so they can be used as nuclear power reactor materials such as fusion reactors, general industrial fields such as engine equipment, and aerospace. The field is expected to be used in high temperature and high pressure environments, and there is a need for methods that provide further structural strengthening of these intermetallic compounds.

  The present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is a method for improving the ductility and strength of NiAl and TiAl intermetallic compounds. The object is to provide a method that does not change the basic structure of the main structure of NiAl and TiAl by adding a large amount of elements.

  As a result of intensive studies to solve the above problems, the present inventors added chromium (Cr) powder as a third element to the raw material powder of intermetallic compound, and subjected high temperature isotropic pressure treatment (HIP) to these mixed powders. It was discovered that the improvement in ductility and strength was observed by applying the present invention, and the present invention was completed.

  That is, the present invention is a method for improving the ductility and strength of an intermetallic compound, and by adding 0-30 mass% of Cr powder to NiAl powder, the resulting intermetallic compound is 873 K and the tensile strength is 200-350 MPa. The strain is about 10% at the maximum.

  The present invention also relates to a method for improving the ductility and strength of an intermetallic compound. By adding 0-30 mass% of Cr powder to NiAl powder, the intermetallic compound obtained is 673K and the tensile strength is 200-600 MPa. The strain is about 2% at the maximum.

  In addition, the present invention is a method for improving the ductility and strength of an intermetallic compound. By adding 0 to 30% by mass of Cr powder to a mixed powder of Ni and Al, the resulting intermetallic compound has a tensile strength of 873K. Is a maximum of 250 MPa and a strain of about 10% at maximum.

  In addition, the present invention provides a high temperature isotropic pressure treatment under the conditions of 973 to 1523 K / 172 to 350 MPa / 2 to 4 hours after adding Cr powder in the above method. The Cr-added mixed powder is sintered by (HIP).

  In addition, the present invention is a method for improving the ductility and strength of an intermetallic compound, and after adding 0 to 30 mass% of Cr powder to TiAl powder, the maximum temperature / maximum pressure / holding time is 1073 to 1473 K / 200. By sintering Cr-added mixed powder by high temperature isostatic pressing (HIP) under conditions of ~ 350MPa / 2 ~ 4 hours, the resulting intermetallic compound has high ductility and strength at high temperatures up to 900K. It is characterized by showing.

  In addition, the present invention is a method for improving the ductility and strength of an intermetallic compound, and after adding 0 to 30 mass% of Cr powder to a mixed powder of Ti and Al, the maximum temperature / maximum pressure / holding time is 1073. By sintering high temperature isostatic pressing (HIP) under the conditions of ~ 1473K / 200 ~ 350MPa / 2 ~ 4 hours, the intermetallic compound obtained is high at high temperatures up to 900K It is characterized by exhibiting ductility and strength.

  Furthermore, the present invention is characterized in that, in any of the methods described above, the high temperature isostatic pressing (HIP) is performed in a multi-stage process over an additional holding time.

  Since the intermetallic compound obtained by the method of the present invention is a low-radiation, corrosion-resistant, high melting point, lightweight material, it can be used as a material for nuclear reactors including nuclear fusion reactors. It can be used in the aerospace field and related industrial fields as engine equipment materials used in the environment.

A method for improving the ductility and strength of the lightweight heat-resistant intermetallic compound of the present invention will be described below.
In the present invention, “lightweight heat-resistant intermetallic compound” refers to a NiAl or TiAl intermetallic compound. The raw materials used in the present invention are prealloyed NiAl or TiAl powder, or simple Ni, Ti, Al powder. Prealloying can be done by conventional techniques in the art. The use of a single powder is effective in that the pre-alloying step can be omitted and the manufacturing cost can be reduced.

  In the present invention, first, NiAl or TiAl powder, which is a starting material, or Ni, Ti and Al powder is refined, and the refined Cr element is added and mixed as a third element in these mixed powders. The addition amount of Cr element should just be 0-30 mass% on the basis of the total mixed powder. The material powder can be refined by a method known in the art, but the powder particle size by refinement is preferably as small as possible from the viewpoint of improving the strength by refinement of the structure.

  Next, the mixed powder is sealed in a capsule and subjected to high temperature isotropic pressure treatment (HIP). Here, the HIP process is a process in which high temperature and high pressure are simultaneously applied, and the element forming the intermetallic compound and the third element Cr element are sintered by the HIP process. The HIP treatment needs to be performed under conditions where Ni or Ti element reacts with Al element and sinters, but Cr element does not react with other elements. The temperature and pressure can be changed with time, but in order to promote sintering, it is preferable to hold both conditions at a maximum for a certain period of time.

  Specifically, when adding Cr element to NiAl powder or mixed powder of Ni and Al elements, it is processed under the conditions of maximum temperature of 973-1523K, maximum pressure of 172-350MPa, holding time of 2-4 hours. I do. By adding 0-30 mass% of Cr powder to NiAl powder and applying the above HIP treatment, the resulting intermetallic compound has a tensile strength of 200-350 MPa at 873K, a strain of up to about 10%, and a tensile strength of 673K. 200 ~ 600MPa, strain up to about 2%. In addition, by adding 0-30% by mass of Cr powder in the mixed powder of Ni and Al and applying the above HIP treatment, the resulting intermetallic compound is 873K, the maximum tensile strength is 250MPa, and the maximum strain is about 10%. Indicates.

  Further, when adding Cr element to the TiAl powder, the treatment is performed under the conditions of a maximum temperature of 1073 to 1473 K, a maximum pressure of 200 to 350 MPa, and a holding time of 2 to 4 hours. By adding 0 to 25% by mass of Cr powder to TiAl powder and performing the above HIP treatment, the resulting intermetallic compound exhibits high ductility and strength at high temperatures up to 900K.

  In another embodiment of the present invention, the HIP process can be performed in a multi-stage process. Here, “multi-stage process” means a process consisting of a plurality of stages in which the maximum temperature and the maximum pressure are held for a certain period of time (steady stage), and then this temperature and pressure are changed and held for a certain period of time (steady stage). Say. When performing multistage processing, additional holding time is required, and the total holding time is usually about 10 hours.

  In the present invention, the reason for adding the Cr element is to improve the mechanical properties of the intermetallic compound after the HIP treatment without changing the basic structure of the main structure of TiAl and NiAl. The object of the present invention is achieved by adding the third element to the main metal in the form of elemental powder instead of the molten material found in the conventional method and performing the HIP treatment.

  The invention is illustrated in more detail by the following examples.

Example 1
A sample was prepared by adding Cr to the NiAl intermetallic compound as a third element and performing HIP treatment. As the NiAl intermetallic compound, NiAl pre-alloy powder or elemental powders of Ni and Al were used. Table 1 shows the composition of the mixed powder in which the Cr addition amount was changed in the range of 0 to 30% by mass.

In the table, (a) is NiAl pre-alloy powder, and (b) is Ni and Al element powder. These mixed powders were subjected to HIP treatment under various treatment conditions shown in FIG.
The mechanical properties of the obtained sintered material were examined. The Vickers hardness was measured by polishing the sample surface, and a tensile test was further performed at a high temperature. The tensile test was performed at a strain rate of 3 × 10 ⁻⁴ s ⁻¹ by controlling the crosshead speed using an Instron type testing machine. The sample was a cylindrical test piece having a diameter of 6 mm and a height of 30 mm, and a sample obtained by forging NiAl was used as a comparative example. FIG. 2 shows the results of the tensile test, FIG. 3 and FIG. 4 show the tensile stress-strain curves, and Table 2 shows the hardness and strain of the samples. FIG. 3 is a tensile stress-strain curve regarding NiAl with x mass% added Cr, and FIG. 4 is Ni + Al with x mass% Cr added.

  In Fig. 2, "HIPed NiAl + xCr" is a NiAl sample with Cr addition amount x mass% with HIP treatment, and "RHIPed NiAl + xCr" is a Ni + Al sample with Cr addition amount x mass% with HIP treatment. And “Forged NiAl” is a forged NiAl sample (Source: G. Wirth, KJ Grundhoff and W. Smarsly: 17th Sample National Technical Conf. On Materials, Kiamesha Lake (USA), 22-24 Oct., (1985) 124 -134). As shown in FIG. 2, a sample having high strength at 673 K was obtained when Cr was added to NiAl powder. NiAl and Ni + Al sintered materials reached the highest high-temperature strength when Cr content was 20%.

In Table 2, RHIP indicates a sample obtained by adding Cr powder to Ni + Al powder and performing HIP treatment.
Example 2
A sample was prepared by adding Cr as a third element to a TiAl intermetallic compound and performing HIP treatment, and this sample was subjected to a tensile test at a high temperature.

  Table 3 shows the composition of the mixed powder using TiAl pre-alloy powder and changing the Cr addition amount in the range of 0 to 30% by mass.

  This mixed powder was subjected to HIP treatment under the treatment conditions shown in FIGS. Fig. 5 shows HIP processing at a maximum pressure of 200MPa and maximum temperature (a) 1273K or (b) 1473K. Fig. 6 (a) shows HIP processing at maximum temperature / maximum pressure / holding time of 1273K / 200MPa / 6 hours. , (B) is a multi-stage HIP process for 1073 K / 250 MPa / 5 hours after the process of (a), and (c) is a multi-stage HIP process for 1073 K / 350 MPa / 5 hours after the process of (a).

  By these treatments, a sintered body having a fine and uniform structure was obtained. The hardness at 1273 K and 200 MPa increased with increasing amount of Cr added at 0 to 25 mass% (not shown).

  The mechanical properties of the obtained sintered body are shown in FIGS. FIG. 7 is a tensile stress-strain curve from room temperature (R.T.) to 1073 K regarding TiAl (TiAl + 5Cr) containing 5 mass% of Cr. The tensile strength was 340 to 380 MPa, and at temperatures higher than 873 K, the strain increased as the temperature increased and the strength decreased. FIG. 8 is a diagram showing the relationship between the tensile strength and temperature of TiAl and TiAl + 5Cr. In the figure, “HIPed TiAl + 5Cr” is a TiAl sample with 5 mass% of Cr added with HIP treatment, “HIPed TiAl” is a TiAl sample with HIP treatment, and “MIMed TiAl” is a sample with TiAl powder injection molded (Source: S. Terachi, T. Teraoka, T. Shinkuma and T. Sugimoto: J. Japan Society of Powder and Powder Metallurgy, 47 (2000) 1283-1287), and "Pure Ti" is untreated Ti It is a simple substance. From these figures, it can be seen that the strength is improved by the method of the present invention. FIG. 9 shows the relationship between strain and temperature. From the figure, it can be seen that the strain of the HIPed TiAl + 5Cr sample according to the present invention is large.

  From the above examples, it was shown that the high temperature strength of the HIP-treated NiAl + Cr material and TiAl material + Cr material of the present invention is improved in ductility and high temperature strength compared to the conventional material.

  The method of the present invention improves the mechanical properties of intermetallic compounds, particularly the ductility and strength. The material obtained by applying the present invention to NiAl and TiAl, which are lightweight heat-resistant intermetallic compounds, can be used as a low-radiation structure material and a lightening structure material. Specifically, it is used for structural materials such as nuclear fusion reactors and general heat-resistant materials, for example, high-performance automobile and marine engine materials, aerospace high-temperature gas turbine blades, engine equipment, and the like.

FIG. 1 is a diagram showing HIP processing conditions for NiAl + Cr and Ni + Al + Cr. FIG. 2 is a diagram showing the relationship between the high temperature strength of NiAl + Cr and Ni + Al + Cr and the amount of Cr added. FIG. 3 is a tensile stress-strain curve regarding NiAl to which x mass% of Cr is added. FIG. 4 is a tensile stress-strain curve regarding Ni + Al to which x mass% of Cr is added. FIG. 5 is a diagram showing the HIP processing conditions of TiAl + Cr, and is processing at a maximum pressure of 200 MPa and a maximum temperature (a) 1273K or (b) 1473K. Fig. 6 is a diagram showing the HIP treatment conditions for TiAl + Cr. (A) is the maximum temperature / maximum pressure / HIP treatment time of 1273K / 200MPa / 6 hours, (b) is after treatment of (a). The multi-stage HIP process for processing at 1073 K / 250 MPa / 5 hours, and (c) is the multi-stage HIP process for processing at 1073 K / 350 MPa / 5 hours after the process in (a). FIG. 7 is a tensile stress-strain curve from room temperature (R.T.) to 1073 K for TiAl to which 5 mass% of Cr is added. FIG. 8 is a diagram showing the relationship between the tensile strength and temperature of TiAl and TiAl + 5Cr. FIG. 9 is a diagram showing the relationship between strain and temperature.

Claims (4)

After adding 20% to 30% by weight of Cr powder to a powder composed of Ni and Al, isotropically applied at high temperature under conditions of a maximum temperature of 973-1523K, a maximum pressure of 172-350 MPa, and a holding time of 2-4 hours A method for improving ductility and strength of an intermetallic compound, characterized by sintering a Cr-added mixed powder by performing a pressure treatment.   2. The method for improving ductility and strength of an intermetallic compound according to claim 1, wherein the powder comprising Ni and Al is a NiAl alloy powder.   The method for improving ductility and strength of an intermetallic compound according to claim 1, wherein the powder comprising Ni and Al is a mixed powder of Ni and Al.   The method for improving ductility and strength of an intermetallic compound according to any one of claims 1 to 3, wherein the high-temperature isotropic pressure treatment is performed in a multi-stage treatment with an additional holding time.

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