Method for homogenizing the compositions and mechanical performances of nickel-based material brazed joints

Abstract

A method for homogenizing the compositions and mechanical performances of nickel-based material brazed joints, includes three homogenized manufacturing steps: Step I, assembling the welding sample, placing it into the vacuum furnace, and then heating up to 830860 C. and holding the temperature; then heating up again to 10501100 C. and holding the temperature; allowing for slow self-cooling in vacuum till it reaches 620640 C.; then filling the furnace with nitrogen and starting the vacuum furnace fan at the same time, so that the sample is cooled down to 4060 C.; Step II, raising the temperature up to 11401160 C. and holding, then cooling it down to the room temperature through water-quenching; Step III, raising the temperature of the welding sample up to 680750 C. again, and cooling it down to the room temperature through air cooling.

Claims

1. A method for homogenizing the compositions and mechanical performances of a nickel-based material brazed joint, the method comprising steps below: Step I: assembling a welding sample and placing the welding sample into a vacuum furnace; first heating up to 830860 C. at a rate of 1316 C./min., and holding the temperature for 3040 min.; then heating up to 10501100 C. at a rate of 710 C./min. and holding the temperature for 2540 min.; allowing for self-cooling in vacuum till the temperature of the sample reaches 620640 C.; then filling the vacuum furnace with nitrogen and starting a vacuum furnace fan at the same time, so that the sample is cooled down to 4060 C.; Step II: raising the temperature of the processed welding sample of Step I up to 11401160 C. and holding the temperature for 1112 h, and then cooling down to a room temperature through water-quenching; Step III: raising the temperature of the processed welding sample of Step II up to 680750 C., holding the temperature for 1719 h, and cooling down to the room temperature through air cooling.

2. The method for homogenizing the composition and mechanical performance of a nickel-based material brazed joint as described in claim 1, wherein the welding sample is made of a nickel-based super alloy material.

3. The method for homogenizing the composition and mechanical performance of a nickel-based material brazed joint as described in claim 1, wherein in Step I, the vacuum furnace is vacuumed to 110.sup.3 Pa.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows the distribution of joint regions on the welding sample before and after homogenization.

DETAILED DESCRIPTION

(2) The welding sample is made of In718, In625 or any other nickel-based super alloy material, which contains Ni, Cr, Mo, Nb, Ti, Al, etc. The brazing material shall be BNi2, with a thickness of 4560 m, containing B, Ni, Cr and so on.

(3) The method for homogenizing the compositions and mechanical performances of nickel-based material brazed joints comprises the following steps:

(4) Step I: First process the base part surfaces through grinding and polishing, followed with acid pickling, alkaline washing, ultrasonic hot water cleaning and acetone washing successively. Then assemble the sample, and vacuum the vacuum furnace to 110.sup.3 Pa.

(5) Put the assembled welding sample into the vacuum furnace; first heat up to 830860 C. at the rate of 1316 C./min., and hold the temperature for 3040 min.; then heat up to 10501100 C. at the rate of 710 C./min. and hold the temperature for 2540 min.; allow for slow self-cooling in vacuum till it drops to 620640 C. from the brazing temperature; then fill the vacuum furnace with nitrogen and start the vacuum furnace fan at the same time, so that the sample is cooled down to 4060 C. and then taken out of the furnace.

(6) This step produces complete solid solution in the brazed joints, so as to eliminate the joint intermediate region, i.e., to remove the borides from the solidified zone of borides, resulting in a relatively strong structure.

(7) Step II:Raise the temperature of the processed welding sample up to 11401160 C. at the rate of 1520 C./min. and hold the temperature for 1112 h; then cool it down to the room temperature via water-quenching;

(8) This step is to decompose the borides of the diffusion zone so that they diffuse to the braze metal and vanish, and to facilitate the diffusion of Nb, Al, Ti and Cr from the braze metal to the brazing seam and enable alloying; by maintaining the temperature for an appropriate time, the chemical compositions of the brazing seam and the braze metal become homogenized, so that the temperature-resistance of joints is enhanced.

(9) Step III: Raise the temperature of the processed welding sample up to 680750 C. at the rate of 1215 C./min, hold the temperature for 1719 h, and cool it down to the room temperature through air cooling.

(10) This step is to produce and phases so that the mechanical properties are further improved.

(11) In the homogenization process in Step II and Step III, B diffuses to the base metal in long range, gets diluted and dissolved in the base metal, improving the mechanical properties.

(12) The three-step homogenization process removes borides from the intermediate zone and diffusion zone at the joints, homogenizes the chemical compositions of the joint and base metal, improves the consistency between mechanical properties of the joint and the base metal, reduces the residual stress, and enhances the high temperature strength of brazed joints. It lays the foundation for achieving the long-cycle reliable operation of plate-fin heat exchangers in the high temperature environment.

(13) FIG. 1 shows the distribution of joint regions before and after homogenization, which can be observed with SEM. The FIGURE shows that, before homogenization, the distribution of borides in the joint's diffusion zone is obvious; after homogenization, these borides are removed, and mechanical properties of the joint and the base metal are homogenized, with the joint's mechanical properties improved.

(14) Table 1 lists the lasting performances of the base metal at 650 C., of the non-homogenized joint and the homogenized joint respectively.

(15) TABLE-US-00001 TABLE 1 Index Time to rupture Elongation at rupture Category (h) (%) Base Metal 39 22 Non-homogenized joint 7 4 Homogenized joint 36 8

(16) From Table 1 it can be seen that the joint's stress-rupture performances are significantly improved after homogenization provided by this disclosure.

(17) Table 2 shows the chemical compositions of the joint's isothermal solidification zone (at. %).

(18) TABLE-US-00002 TABLE 2 Element Stage/zone Ni Cr No Nb + Al + Ti Before Solidified zone 69 11.8 0 0 homogenization Base metal 46.2 18.2 3.1 6.4 After Solidified zone 54 19 1.8 5.5 homogenization Base metal 51 17 2.1 5.9

(19) From Table 2 it can be seen that after the homogenization provided by this disclosure, the chemical composition contents in the joint and base metal changes substantially and become homogenized.