Background technology
During electrochemical etching, processed sample as anode, is added the voltage of certain intensity between anode and cathode, anode sample dissolution then, crystal grain and grain boundary expose out, thereby can obtain the picture of metallographic structure.Its mechanism of generally acknowledging is to form one deck polarized film on the metal anode surface, make metallic ion pass through this layer film diffusion, the height point at lip-deep micro-and macroscopical salient point or coarse place and the current density specific surface remainder in burr district are big, and with fast speeds dissolving, thereby reach the purpose of leveling and deburring.Can regulate the crystal grain dissolution velocity by experiment conditions such as control polishing time, experimental temperature and current densities, obtain surface clean, crystal boundary is the metallographic structure photo clearly.
Nickel-base alloy is widely used in the deep-etching Service Environment such as oil and natural gas because of its excellent corrosion resistance and outstanding physical and mechanical properties.But the problem that incident its metallographic is difficult for making has brought a difficult problem for our the optimization research work of material.CN1167839 discloses a kind of patented claim of metallographic etching agent, is applicable to the etching pit of high copper-titanium alloy (C u content weight ratio is greater than 10%).CN101104935 discloses a kind of patented claim of metallographic etching agent, is done and water is formed by hydrofluorite, nitric acid, acetone, acetic acid.Adopt it can make metallographic observation face light, the metallographic structure crystal boundary is clear, tells α phase or other precipitated phase that disperse is separated out easily, is particularly suitable for the metallographic etching agent as the nearly β of aging state, metastable beta-titanium alloy.Yet adopt the chemical method etch for nickel-base alloy, its metallographic is often wayward because of the etch time, and causes gained metallographic readability not good enough, and prepared metallographic structure is difficult to differentiate; The research of the electrochemical etching aspect of nickel-base alloy rarely has report, therefore has a large amount of blank to remain to be filled in this field.
Summary of the invention
The object of the present invention is to provide a kind of electrochemical metallographic etching method of universal for nickel-based alloys, make the oxidation of nickel-base alloy corrosion-resistant easy, thereby obtain the metallographic structure of nickel-base alloy easily, sharpness is higher simultaneously.
Electrochemical metallographic etching method of the present invention is a conducting medium with metallographic etching liquid, is anode with the nickel-base alloy metallographic specimen, is negative electrode with the platinum electrode, and the etch condition is: etch voltage constant voltage 2V/cm
2-8V/cm
2, etch time 1min-5min.
Metallographic etching liquid involved in the present invention is by weight percentage: contain phosphoric acid 65%-85%, sulfuric acid 5%-15%, chromic acid 8%-15%, glycerine 3%-8%.
The G-3 that the present invention makes, 825, high temperature ni-resist base alloy metallograph surfacings such as X750, crystal boundary is clearly demarcated, and crystal grain is clear, is applicable to that Ni-Fe-Cr is an alloy.
The compound method of this electrochemical metallographic etching liquid is simple, and effect is remarkable.Compare chemical metallographic etching method, the easier control of electrochemical method condition, experimental repeatability is good, and the metallograph that makes is clear.
Embodiment
With reference to the accompanying drawings and in conjunction with example the present invention and implementation result are further described below.
Embodiment 1: in the sampling of G-3 alloy oil pipe outside surface, it is carried out the experiment of electrochemical method etch metallographic
1, parallels to the axis at G-3 oil pipe outside surface with the electric spark patterning method that to cut area be 1x1cm to direction
2, thickness is the square sample of 2mm.
2, at sample back side welding lead, be panel with ethylenediamine-epoxy resin then, inlay sample.Encapsulation makes the cylindricality sample that radius is 20mm.
3, polish sample step by step to its smooth surface with waterproof abrasive paper, and remove the polishing scratch that stays by fine grinding on the metallographic specimen flour milling, become smooth flawless minute surface with mechanical polishing method.
4, metallographic etching liquid adopts prescription involved in the present invention to be: phosphoric acid 65%, sulfuric acid 15%, chromic acid 15%, glycerine 5% (percentage by weight).
5, adopting the constant voltage/constant current source is the decomposition voltage source.Experimental sample links to each other with positive source, and power cathode connects platinum electrode.With this metallographic etching liquid is conducting medium, connects electrochemical etching metallographic device.Control etch condition constant voltage is 4.5V/cm
2, the etch time is 2min.Make G-3 oil pipe outside surface metallograph as shown in Figure 4.
Embodiment 2: in the sampling of G-3 alloy pipe inner surface, it is carried out the experiment of electrochemical method etch metallographic
1, parallels to the axis at the G-3 pipe inner surface with the electric spark patterning method that to cut area be 1x1cm to direction
2, thickness is the square sample of 2mm.
2, at sample back side welding lead, be panel with ethylenediamine-epoxy resin then, inlay sample.Encapsulation makes the cylindricality sample that radius is 20mm.
3, polish sample step by step until its smooth surface with waterproof abrasive paper, and remove the polishing scratch that stays by fine grinding on the metallographic specimen flour milling, become smooth flawless minute surface with mechanical polishing method.
4, metallographic etching liquid adopts prescription involved in the present invention to be: phosphoric acid 84%, sulfuric acid 5%, chromic acid 8%, glycerine 3% (percentage by weight).
5, adopting the constant voltage/constant current source is the decomposition voltage source.Experimental sample links to each other with positive source, and power cathode connects platinum electrode.With this metallographic etching liquid is conducting medium, connects electrochemical etching metallographic device.Control etch condition constant voltage is 6V/cm
2, the etch time is 1.5min.Make G-3 oil pipe outside surface metallograph as shown in Figure 5.
Embodiment 3: in the sampling of Incoloy 825 alloy oil pipe outside surfaces, adopt the present invention that it is carried out the experiment of electrochemical method etch metallographic
1, parallel to the axis at Incoloy 825 oil pipe outside surfaces with the electric spark patterning method that to cut area be 1x1cm2 to direction, thickness is the square sample of 2mm.
2, at sample back side welding lead, be panel with ethylenediamine-epoxy resin then, inlay sample.Encapsulation makes the cylindricality sample that radius is 20mm.
3, polish sample step by step until its smooth surface with waterproof abrasive paper, and remove the polishing scratch that stays by fine grinding on the metallographic specimen flour milling, become smooth flawless minute surface with mechanical polishing method.
4, metallographic etching liquid adopts prescription involved in the present invention to be: phosphoric acid 65%, sulfuric acid 5%, chromic acid 15%, glycerine 15% (percentage by weight).
5, adopting the constant voltage/constant current source is the decomposition voltage source.Experimental sample links to each other with positive source, and power cathode connects platinum electrode.With this metallographic etching liquid is conducting medium, connects electrochemical etching metallographic device.Control etch condition constant voltage is 3.5V/cm
2, the etch time is 3min.Make G-3 oil pipe outside surface metallograph as shown in Figure 6.
For detecting the invention process effect, select etch nickel-base alloy Inconel Alloy G-3 metallographic to be the contrast experiment, condition is respectively 10g iron chloride+30ml concentrated hydrochloric acid+20ml water, chemical etching, as shown in Figure 1; 5ml nitric acid+25ml concentrated hydrochloric acid+30ml water, chemical etching, as shown in Figure 2; 30ml sulfuric acid+20ml water, electrochemical etching, as shown in Figure 3.
Fig. 4 that embodiment 1-3 obtains-Fig. 6 comparison diagram 1, Fig. 2, it is clear obviously to find out through grain boundary in the prepared metallograph of electrochemical etching method, tissue topography can be complete present, and eliminated simple chemical etching method because the etch time is difficult to grasp the defective of the peroxidating (stain, blackspot) that is occurred.Comparison diagram 3, the electrochemical etching liquor ratio sulfuric acid of being announced among the present invention as can be seen are that etching solution has more excellent metallographic and prepares effect.To sum up, the present invention a kind ofly has the electrochemical metallographic etching method that good metallographic structure prepares effect for nickel-base alloy.