Corrosion observation method for molybdenum alloy microstructure

Abstract

The invention discloses a corrosion observation method for a molybdenum alloy microstructure. The method comprises the following steps: 1, machining a molybdenum alloy to form a microstructure observation plane, grinding, and washing off sand grains; 2, carrying out mechanical polishing until the surface of the microscopic structure observation plane is free of scratches and dragging; 3, immersing into an etchant solution to erode; and 4, observing a metallographic structure under a metallographic microscope. By controlling the components and proportion of the corrosion solution, the microstructure in the molybdenum alloy is clear, has obvious grain boundary and no obvious corrosion pit, is convenient for metallographic microscope observation, and achieves the same or similar corrosion effect on the molybdenum alloy on the premise of not using potassium ferricyanide; the situation that highly toxic potassium cyanide generated by decomposition in an existing corrosion solution harms personal safety is avoided, and the observation method is easy to operate, free of poison, free of special equipment and easy to popularize.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material microstructure observation, and in particular relates to a corrosion observation method for molybdenum alloy microstructure. Background Art

[0002] Molybdenum has the characteristics of high melting point, low thermal expansion coefficient, high high temperature strength and low high temperature creep rate. It is widely used in aerospace, nuclear energy, medical electronics and other fields. The main components of MHC molybdenum alloy are molybdenum-(0.8~1.2)Hf-(0.05~0.12)C. The main methods for producing MHC molybdenum alloy in industry are powder metallurgy and smelting. The smelting method is to melt pure molybdenum and a certain amount of hafnium and carbon elements under vacuum, and obtain MHC molybdenum alloy through hot deformation and annealing; the MHC molybdenum alloy prepared by smelting method has coarse grains and is prone to component segregation. The MHC molybdenum alloy prepared by powder metallurgy has a fine-grained structure and can save large equipment such as vacuum consumable arc furnaces, extruders and high-temperature heating furnaces, thereby simplifying the production process, shortening the production cycle, reducing production consumption, and improving production capacity and yield rate. Molybdenum alloys usually need to observe the alloy microstructure and evaluate the average grain size level in order to accurately evaluate the organization of molybdenum alloys.

[0003] At present, molybdenum alloys are mainly corroded by a mixed solution of potassium ferrocyanide and sodium hydroxide to display the structure of molybdenum alloy samples. However, the decomposition of potassium ferrocyanide will produce potassium cyanide, which is a highly toxic substance and threatens the safety of test personnel. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for corrosion observation of molybdenum alloy microstructure in view of the above-mentioned deficiencies of the prior art. The method controls the components and proportions of the corrosive solution, so that the microstructure in the molybdenum alloy is clear, with obvious grain boundaries and no obvious corrosion pits, which is convenient for metallographic microscope observation, and achieves the same or similar corrosion effect on the molybdenum alloy without using potassium ferrocyanide, thereby solving the problem that the existing corrosive solution decomposes to produce highly toxic potassium cyanide that endangers personal safety.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a corrosion observation method for molybdenum alloy microstructure, characterized in that the method comprises the following steps:

[0006] Step 1: Mechanically process the molybdenum alloy into a microstructure observation plane, then grind the machined microstructure observation plane on a metallographic grinder, and wash away the sand on the microstructure observation plane after grinding;

[0007] Step 2: placing the microstructure observation plane washed away with sand in step 1 on a polishing machine for mechanical polishing until there are no scratches or drag on the surface of the microstructure observation plane;

[0008] Step 3, immersing the microstructure observation plane after mechanical polishing in step 2 into a corrosive solution for 10s to 30s;

[0009] Step 4: Place the microstructure observation plane after etching in step 3 under a metallographic microscope, and observe the metallographic structure by open field observation.

[0010] The present invention processes the molybdenum alloy into a microstructure observation plane, then grinds the microstructure observation plane flat, and rinses to remove the abrasive particles and dust brought by grinding, so as to provide a sufficiently smooth foam for subsequent polishing, and then uses a corrosive solution to erode the molybdenum alloy to display its microstructure. Different from the current molybdenum alloy mainly corroded by a mixed solution of potassium ferrocyanide and sodium hydroxide, but potassium ferrocyanide is unstable in water and easily decomposed by light to produce highly toxic cyanide, the corrosive solution of the present invention achieves the same or similar corrosion effect on the molybdenum alloy without using potassium ferrocyanide, thereby avoiding the generation of highly toxic substances that harm the human body and the environment. At the same time, the present invention aims at the problem that aqua regia composed of concentrated nitric acid and concentrated hydrochloric acid has a uniform corrosion effect on the molybdenum alloy but cannot display the microstructure. On the basis of adding concentrated nitric acid and concentrated hydrochloric acid components to the corrosion solution, hydrofluoric acid and sulfuric acid components are selectively added, and the proportion of each component is adjusted, so as to accelerate the reaction rate of the corrosion solution and the molybdenum alloy during the erosion process on the one hand, and control the corrosion effect of the corrosion solution on the molybdenum alloy on the other hand, that is, the corrosion rate of the grain boundary is fast and the corrosion rate of the internal structure of the grain is slow, so that the grain boundary of the molybdenum alloy is deeply corroded after the erosion, and the grain boundary shows a darker color under an optical microscope, so that it is convenient to observe the microstructure of the molybdenum alloy.

[0011] The above-mentioned method for observing the corrosion of molybdenum alloy microstructure is characterized in that the specific process of grinding in step 1 is: using a particle size of 120 # , 400 # , 800# and 1000 # The metallographic water sandpaper is used for grinding step by step. Each time the metallographic water sandpaper is changed for grinding, the grinding direction is turned 90° to ensure that the previous grinding marks are completely eliminated.

[0012] The above-mentioned method for corrosion observation of molybdenum alloy microstructure is characterized in that the mechanical polishing in step 2 is firstly rough polishing using a diamond suspension with a particle size of 10 μm, and then fine polishing using a diamond suspension with a particle size of 1 μm.

[0013] The above-mentioned corrosion observation method of molybdenum alloy microstructure is characterized in that the corrosion solution in step three is composed of the following components in volume fractions: 2 to 4 parts of HF with a mass fraction of more than 40%, 0.5 to 1 part of HNO3 with a mass fraction of 65% to 68%, 0.5 to 1 part of H2SO4 with a mass fraction of 95% to 98%, and 2 to 4 parts of HCl with a mass fraction of 36% to 38%. Since the sulfuric acid component of the corrosion solution is concentrated sulfuric acid, hydrofluoric acid, nitric acid and concentrated sulfuric acid are first mixed during preparation, and hydrochloric acid is finally added to prevent splashing. The corrosion solution significantly accelerates the corrosion rate and improves the corrosion effect by adding the concentrated sulfuric acid component, so that the molybdenum alloy shows a better corrosion effect in a short time.

[0014] The above-mentioned method for corrosion observation of molybdenum alloy microstructure is characterized in that the HF, HNO3, H2SO4 and HCl are all analytically pure reagents.

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

[0016] 1. The present invention processes the molybdenum alloy into a microstructure observation plane and then grinds, rinses, mechanically polishes and corrodes with a corrosive solution in sequence. By controlling the components and proportions of the corrosive solution, the microstructure in the molybdenum alloy is clear, with obvious grain boundaries and no obvious corrosion pits, which is convenient for metallographic microscope observation. The same or similar corrosion effect on the molybdenum alloy is achieved without using potassium ferrocyanide.

[0017] 2. The present invention adopts an acid solution composed of HF, HNO3, H2SO4 and HCl for corrosion, without the need to use potassium ferrocyanide and sodium hydroxide, thus avoiding the problem of the existing molybdenum alloy microstructure corrosion method decomposing and producing highly toxic potassium cyanide, avoiding the threat to personal safety, being easy to operate, non-toxic, and requiring no special equipment, and being easy to promote.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the metallographic structure diagram of the molybdenum alloy in Example 1 of the present invention.

[0020] Figure 2 This is the metallographic structure diagram of the molybdenum alloy in Example 2 of the present invention.

[0021] Figure 3 This is the metallographic structure diagram of the molybdenum alloy in Example 3 of the present invention.

[0022] Figure 4 This is the metallographic structure diagram of the molybdenum alloy in Example 4 of the present invention.

[0023] Figure 5This is the metallographic structure diagram of the molybdenum alloy in Example 5 of the present invention. DETAILED DESCRIPTION

[0024] Example 1

[0025] This embodiment includes the following steps:

[0026] Step 1: Mechanically process the molybdenum alloy into a microstructure observation plane, then grind the machined microstructure observation plane on a metallographic grinder, and wash away the sand on the microstructure observation plane after grinding; the specific process of the grinding is: using a particle size of 120 # , 400 # , 800# and 1000 # Grind step by step with metallographic water sandpaper. Each time you change the metallographic water sandpaper for grinding, turn the grinding direction 90° to ensure that the last grinding marks are completely eliminated.

[0027] Step 2: placing the microstructure observation plane washed away from the sand in step 1 on a polishing machine for mechanical polishing until there are no scratches and drags on the surface of the microstructure observation plane; the mechanical polishing is firstly rough polishing with a diamond suspension with a particle size of 10 μm, and then fine polishing with a diamond suspension with a particle size of 1 μm;

[0028] Step 3, immersing the microstructure observation plane after mechanical polishing in step 2 into a corrosion solution for 18 seconds; the corrosion solution is composed of the following components in volume fractions: 3 parts of HF with a mass fraction of more than 40%, 1 part of HNO3 with a mass fraction of 65% to 68%, 1 part of H2SO4 with a mass fraction of 95% to 98%, and 4 parts of HCl with a mass fraction of 36% to 38%, and HF, HNO3, H2SO4 and HCl are all analytically pure reagents;

[0029] Step 4: Place the microstructure observation plane after etching in step 3 under a metallographic microscope, and observe the metallographic structure by open field observation.

[0030] Figure 1 is the metallographic structure diagram of the molybdenum alloy in this embodiment, Figure 1 The irregular lines in the figure are grain boundaries, and the black particles are the precipitated phases of molybdenum alloy. Figure 1 It can be seen that the metallographic structure of the molybdenum alloy has obvious grain structure and no obvious corrosion pits.

[0031] Example 2

[0032] This embodiment includes the following steps:

[0033] Step 1: Mechanically process the molybdenum alloy into a microstructure observation plane, then grind the machined microstructure observation plane on a metallographic grinder, and wash away the sand on the microstructure observation plane after grinding; the specific process of the grinding is: using a particle size of 120 # , 400 # , 800# and 1000 # Grind step by step with metallographic water sandpaper. Each time you change the metallographic water sandpaper for grinding, turn the grinding direction 90° to ensure that the last grinding marks are completely eliminated.

[0034] Step 2: placing the microstructure observation plane washed away from the sand in step 1 on a polishing machine for mechanical polishing until there are no scratches and drags on the surface of the microstructure observation plane; the mechanical polishing is firstly rough polishing with a diamond suspension with a particle size of 10 μm, and then fine polishing with a diamond suspension with a particle size of 1 μm;

[0035] Step 3, immersing the microstructure observation plane after mechanical polishing in step 2 into a corrosion solution for 25 seconds; the corrosion solution is composed of the following components in volume fractions: 2 parts of HF with a mass fraction of more than 40%, 0.5 parts of HNO3 with a mass fraction of 65% to 68%, 0.5 parts of H2SO4 with a mass fraction of 95% to 98%, and 2 parts of HCl with a mass fraction of 36% to 38%, and HF, HNO3, H2SO4 and HCl are all analytically pure reagents;

[0036] Step 4: Place the microstructure observation plane after etching in step 3 under a metallographic microscope, and observe the metallographic structure by open field observation.

[0037] Figure 2 is the metallographic structure diagram of the molybdenum alloy in this embodiment, Figure 2 The irregular lines in the figure are grain boundaries, and the black particles are the precipitated phases of molybdenum alloy. Figure 2 It can be seen that the metallographic structure of the molybdenum alloy has obvious grain structure and no obvious corrosion pits.

[0038] Example 3

[0039] This embodiment includes the following steps:

[0040] Step 1: Mechanically process the molybdenum alloy into a microstructure observation plane, then grind the machined microstructure observation plane on a metallographic grinder, and wash away the sand on the microstructure observation plane after grinding; the specific process of the grinding is: using a particle size of 120 # , 400 # , 800# and 1000 #Grind step by step with metallographic water sandpaper. Each time you change the metallographic water sandpaper for grinding, turn the grinding direction 90° to ensure that the last grinding marks are completely eliminated.

[0041] Step 2: placing the microstructure observation plane washed away from the sand in step 1 on a polishing machine for mechanical polishing until there are no scratches and drags on the surface of the microstructure observation plane; the mechanical polishing is firstly rough polishing with a diamond suspension with a particle size of 10 μm, and then fine polishing with a diamond suspension with a particle size of 1 μm;

[0042] Step 3, immersing the microstructure observation plane after mechanical polishing in step 2 in a corrosion solution for 20 seconds; the corrosion solution is composed of the following components in volume fractions: 2 parts of HF with a mass fraction of more than 40%, 1 part of HNO3 with a mass fraction of 65% to 68%, 1 part of H2SO4 with a mass fraction of 95% to 98%, and 2 parts of HCl with a mass fraction of 36% to 38%, and HF, HNO3, H2SO4 and HCl are all analytically pure reagents;

[0043] Step 4: Place the microstructure observation plane after etching in step 3 under a metallographic microscope, and observe the metallographic structure by open field observation.

[0044] Figure 3 is the metallographic structure diagram of the molybdenum alloy in this embodiment, Figure 3 The irregular lines in the figure are grain boundaries, and the black particles are the precipitated phases of molybdenum alloy. Figure 3 It can be seen that the metallographic structure of the molybdenum alloy has obvious grain structure and no obvious corrosion pits.

[0045] Example 4

[0046] This embodiment includes the following steps:

[0047] Step 1: Mechanically process the molybdenum alloy into a microstructure observation plane, then grind the machined microstructure observation plane on a metallographic grinder, and wash away the sand on the microstructure observation plane after grinding; the specific process of the grinding is: using a particle size of 120 # , 400 # , 800# and 1000 # Grind step by step with metallographic water sandpaper. Each time you change the metallographic water sandpaper for grinding, turn the grinding direction 90° to ensure that the last grinding marks are completely eliminated.

[0048] Step 2: placing the microstructure observation plane washed away from the sand in step 1 on a polishing machine for mechanical polishing until there are no scratches and drags on the surface of the microstructure observation plane; the mechanical polishing is firstly rough polishing with a diamond suspension with a particle size of 10 μm, and then fine polishing with a diamond suspension with a particle size of 1 μm;

[0049] Step 3, immersing the microstructure observation plane after mechanical polishing in step 2 into a corrosion solution for 10 seconds; the corrosion solution is composed of the following components in volume fractions: 2 parts of HF with a mass fraction of more than 40%, 1 part of HNO3 with a mass fraction of 65% to 68%, 1 part of H2SO4 with a mass fraction of 95% to 98%, and 2 parts of HCl with a mass fraction of 36% to 38%, and HF, HNO3, H2SO4 and HCl are all analytically pure reagents;

[0050] Step 4: Place the microstructure observation plane after etching in step 3 under a metallographic microscope, and observe the metallographic structure by open field observation.

[0051] Figure 4 is the metallographic structure diagram of the molybdenum alloy in this embodiment, Figure 4 The irregular lines in the figure are grain boundaries, and the black particles are the precipitated phases of molybdenum alloy. Figure 4 It can be seen that the metallographic structure of the molybdenum alloy has obvious grain structure and no obvious corrosion pits.

[0052] Example 5

[0053] This embodiment includes the following steps:

[0054] Step 1: Mechanically process the molybdenum alloy into a microstructure observation plane, then grind the machined microstructure observation plane on a metallographic grinder, and wash away the sand on the microstructure observation plane after grinding; the specific process of the grinding is: using a particle size of 120 # , 400 # , 800# and 1000 # Grind step by step with metallographic water sandpaper. Each time you change the metallographic water sandpaper for grinding, turn the grinding direction 90° to ensure that the last grinding marks are completely eliminated.

[0055] Step 2: placing the microstructure observation plane washed away from the sand in step 1 on a polishing machine for mechanical polishing until there are no scratches and drags on the surface of the microstructure observation plane; the mechanical polishing is firstly rough polishing with a diamond suspension with a particle size of 10 μm, and then fine polishing with a diamond suspension with a particle size of 1 μm;

[0056] Step 3, immersing the microstructure observation plane after mechanical polishing in step 2 into a corrosion solution for 30 seconds; the corrosion solution is composed of the following components in volume fractions: 4 parts of HF with a mass fraction of more than 40%, 2 parts of HNO3 with a mass fraction of 65% to 68%, 1 part of H2SO4 with a mass fraction of 95% to 98%, and 4 parts of HCl with a mass fraction of 36% to 38%, and HF, HNO3, H2SO4 and HCl are all analytically pure reagents;

[0057] Step 4: Place the microstructure observation plane after etching in step 3 under a metallographic microscope, and observe the metallographic structure by open field observation.

[0058] Figure 5 is the metallographic structure diagram of the molybdenum alloy in this embodiment, Figure 5 The irregular lines in the figure are grain boundaries, and the black particles are the precipitated phases of molybdenum alloy. Figure 5 It can be seen that the metallographic structure of the molybdenum alloy has obvious grain structure and no obvious corrosion pits.

[0059] 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 observing corrosion of molybdenum alloy microstructure, characterized in that: The method comprises the following steps: Step 1: Mechanically process the molybdenum alloy into a microstructure observation plane, then grind the machined microstructure observation plane on a metallographic grinder, and wash away the sand on the microstructure observation plane after grinding; Step 2: placing the microstructure observation plane washed away with sand in step 1 on a polishing machine for mechanical polishing until there are no scratches or drag on the surface of the microstructure observation plane; Step 3, immersing the microstructure observation plane after mechanical polishing in step 2 into a corrosive solution for 10s to 30s; Step 4: Place the microstructure observation plane after etching in step 3 under a metallographic microscope, and observe the metallographic structure by open field observation.

2. The corrosion observation method of a molybdenum alloy microstructure according to claim 1, characterized in that: The specific process of grinding in step 1 is: using a particle size of 120 # , 400 # , 800# and 1000 # The metallographic water sandpaper is used for grinding step by step. Each time the metallographic water sandpaper is changed for grinding, the grinding direction is turned 90° to ensure that the previous grinding marks are completely eliminated.

3. The corrosion observation method of a molybdenum alloy microstructure according to claim 1, characterized in that: The mechanical polishing in step 2 is firstly rough polishing with a diamond suspension having a particle size of 10 μm, and then fine polishing with a diamond suspension having a particle size of 1 μm.

4. The corrosion observation method of a molybdenum alloy microstructure according to claim 1, characterized in that: The etching solution in step 3 is composed of the following components in parts by volume: 2 to 4 parts of HF with a mass fraction of more than 40%, 0.5 to 1 part of HNO3 with a mass fraction of 65% to 68%, 0.5 to 1 part of H2SO4 with a mass fraction of 95% to 98%, and 2 to 4 parts of HCl with a mass fraction of 36% to 38%.

5. The corrosion observation method of a molybdenum alloy microstructure according to claim 4, characterized in that: The HF, HNO3, H2SO4 and HCl are all analytically pure reagents.

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