Dense thick alloy coating without layered organizational structure and preparation method thereof

Abstract

A dense thick alloy coating with no layered organizational structure and a preparation method thereof are provided. The preparation method includes the following steps: step 1, placing a substrate in a plasma spraying apparatus, controlling a vacuum degree of the plasma spraying apparatus to be 0.2 mbar-0.5 mbar, controlling a length of a plasma flame of the plasma spraying apparatus to be 1000 mm-1200 mm, and controlling a diameter of the plasma flame to be 200 mm-300 mm; step 2, preheating, by using a plasma spray gun, the substrate to a temperature of 700° C.-1000° C. to obtain a preheated substrate; step 3, plasma spraying an alloy powder on the preheated substrate under a specific plasma spraying condition to obtain a sprayed substrate; and step 4, cooling the sprayed substrate after the plasma spraying, to thereby obtain the dense thick alloy coating without layered organizational structure.

1 . A preparation method of a dense alloy coating without layered organizational structure, wherein no layered organizational structure exists in the dense alloy coating, an edge of the dense alloy coating has no cracking and warping, a thickness of the dense alloy coating is in a range from 2 millimeters (mm) to 3.5 mm, and the preparation method comprises:
 step 1, placing a substrate in a plasma spraying apparatus, controlling a vacuum degree of the plasma spraying apparatus to be in a range from 0.2 millibars (mbar) to 0.5 mbar, controlling a length of a plasma flame of the plasma spraying apparatus to be in a range from 1000 mm to 1200 mm, and controlling a diameter of the plasma flame to be in a range from 200 mm to 300 mm;   step 2, preheating, by using a plasma spray gun, the substrate to a temperature in a range from 700 degrees Celsius (° C.) to 1000° C. to obtain a preheated substrate;   step 3, plasma spraying an alloy powder on the preheated substrate to obtain a sprayed substrate, wherein conditions of the plasma spraying comprise: a spraying power is in a range from 80 kilowatts (kw) to 130 kw, a powder feeding speed is in a range from 10 grams per minute (g/min) to 30 g/min, a spraying distance is in a range from 450 mm to 800 mm, and a relative linear velocity between the plasma flame and a surface of the substrate is in a range from 1 meter per second (m/s) to 3 m/s; the alloy powder satisfies the following requirements: a particle size of the alloy powder is smaller than 40 micrometers (μm), and an oxygen content of the alloy powder is less than 600 parts per million (ppm); and the alloy powder comprises at least one selected from the group consisting of NiCoCrAlY, NiCrAlY, NiAl, NiAlW, CoCrW, and CoCrMoSi; and   step 4, cooling the sprayed substrate after the plasma spraying, to thereby obtain the dense alloy coating without layered organizational structure.   
     
     
         2 . The preparation method according to  claim 1 , wherein in the step 1, the controlling a vacuum degree of the plasma spraying apparatus to be in a range from 0.2 mbar to 0.5 mbar comprises:
 vacuuming a vacuum chamber in which the substrate is placed of the plasma spraying apparatus to control a vacuum degree of the vacuum chamber to be in a range from 0.005 mbar to 0.01 mbar, filling argon into the vacuum chamber to control the vacuum degree of the vacuum chamber to be in a range from 50 mbar to 100 mbar, re-vacuuming the vacuum chamber to control the vacuum degree of the vacuum chamber to be in a range from 0.005 mbar to 0.01 mbar, and refilling argon into the vacuum chamber to control the vacuum degree of the vacuum chamber to be in the range from 0.2 mbar to 0.5 mbar.   
     
     
         3 . The preparation method according to  claim 1 , wherein the step 1 further comprises: before placing the substrate in the plasma spraying apparatus, performing a roughening treatment on the surface of the substrate. 
     
     
         4 . The preparation method according to  claim 3 , wherein a roughness Ra of the surface of the substrate is in a range from 6 μm to 8 μm through the roughening treatment. 
     
     
         5 . The preparation method according to  claim 1 , wherein in the step 2, the preheating, by using a plasma spray gun, the substrate comprises:
 performing blowing and preheating the surface of the substrate by using a flame from the plasma spray gun, wherein a power of the plasma spray gun is controlled to be in a range from 60 kw to 150 kw, a blowing distance for the blowing is in a range from 200 mm to 500 mm, a blowing speed for the blowing is in a range from 200 millimeters per second (mm/s) to 1000 mm/s, and a preheating time for the preheating is in a range from 3 minutes (min) to 8 min.   
     
     
         6 . The preparation method according to  claim 1 , wherein in the step 4, a cooling speed for the cooling is in a range from 5 degrees Celsius per minute (° C./min) to 40° C./min, and a cooling time for the cooling is in a range from 20 min to 60 min. 
     
     
         7 . The preparation method according to  claim 6 , wherein the cooling is performed through a plurality of gradient cooling stages, and a difference between a cooling speed of a latter gradient cooling stage of the plurality of gradient cooling stages and a cooling speed of a former gradient cooling stage of the plurality of gradient cooling stages is in a range from 5° C./min to 20° C./min. 
     
     
         8 . (canceled) 
     
     
         9 . The preparation method according to  claim 1 , wherein
 a porosity of the dense alloy coating without layered organizational structure is less than 1%, an oxygen content of the dense alloy coating without layered organizational structure is less than 0.1%; and a bonding strength of the dense alloy coating without layered organizational structure is greater than 70 megapascals (MPa).