SU966546A1 - Method of preparing surface of easy-passivating metals and alloys for investigating their structure - Google Patents

Description

The invention relates to the metallurgy of non-ferrous metals and can be used in the preparation of the surface of lightly passivating metals and alloys, including titanium, niobium, zirconium, and hafnium, for the study of their structure by metallographic, electron microscopic X-ray, micro X-ray spectroscopic methods widely used in mechanical engineering, aircraft building, rocket science, metallurgy. There are known methods for obtaining objects for the study of the structure of mechanical IMM by grinding and polishing, electrochemical polishing 1. However, mechanical grinding and polishing causes surface hardening and is not very productive, electrochemical, polishing requires very strict regulation of the current treatment modes and the composition of solutions. The closest to the invention is a method of preparing the surface by a chemical method, including the operation of mechanical grinding and chemical polishing of grinding samples of titanium in boiling orthophosphoric acid 2. A disadvantage of the known method is that providing polishing, it is not able to simultaneously detect real surface relief of different phases with all the details of micro, sub and fine structure. This method is only preparatory and not final when preparing the objects for the study of the structure, since after chemical polishing, subsequent additional etching is required in special reagents according to certain conditions. The purpose of the invention is the detection of micro, sub and fine structures with a high degree of resolution of parts with sizes up to 0.1 µm. This goal is achieved in that according to the method of preparing the surface of easily digestible metals and alloys to study their structure, including mechanical grinding and chemical polishing, the latter is carried out alternately by repeatedly immersing the sample in concentrated solutions of first hydrogen peroxide and then a mixture of hydrofluoric and nitric acids.

taken in the ratio (2-3): 1, with a dwell time of 0.5-3.0 s.

In this case, the sample is alternately immersed in the solution 3-30 times.

Immersion in a concentrated melt solution (vikovoy and nitric acids in the ratio (/ -3): 1 with a dwell time of 0.5-3 s, ensures first a uniform dissolution of the old oxide film and a thin metal surface layer with the detection of the elements of the microstructure (phase boundaries, .sepeii, discontinuities), substructures (grain boundaries, polygons, sko / zhzheni lines, twinning), fine cTpy paths (dislocations, traces of their interaction, growth steps) and subsequent almost simultaneously passaging, as a result of which ited formed of the metal thin protective film is new. The concentrated sol hydrogen peroxide before treatment ochtsschaet surface of fat, moisture, impurities, and thereafter the passivation effect increases with the fixation surface structure.

Alternating multiple (330 cycles) immersion into the indicated solutions provides a gradual unsharp uniform dissolution of the sample with the detection of all elements of the micro, sub and fine structure and the growth of the passive film.

Table 1 presents data on the effect of the exposure time on the character of the identified structure according to the proposed method.

Table 1

less than 0.5

- Not detected

0.1 You are incomplete, 0.5

1.0 0, 1 You are clearly with many 0, 1 You are clearly with many 2, 0

0.1 You are cycling

3.0 4.0

2.0 Overtravel appears

29 Active Pitting, re 10, 0

Table 2 shows the comparative experimental data of the known

multiple cycling is necessary (30 cycles) multiple cycles (7-20 cycles) multiple cycles (5-15 cycles) (3-7 cycles) single pits, bottled, grain boundaries, phases etched, blurred many elements of the structure

and the proposed methods with a different ratio of acids in the mixture.

one

Not detected

1.0 Elements of the structure revealed indistinct,: grain and phase boundaries are discontinuous, poorly pronounced

0.1 Grain phase boundaries, continuous, clearly defined elements. fine structure /

less clearly the elements of the substructure

0.1 Phase grain boundaries. clear continuous, well-defined elements of fine structure and substructure

3-10 Peretravlena, the elements of the structure are blurred, broadened, the clarity of the transition between the discharge of the phases is violated

:one

10-20 Strongly overtrained, the elements of the structure are blurred, enlarged, fuzzy, the clarity of the transition between phases is completely disrupted.

Example 1. A sample surface of a titanium alloy with 0.3% oxygen, ground to a roughness of Ry 1.5, is treated alternately in concentrated hydrogen peroxide and a mixture of hydrofluoric and nitric acids taken in a ratio of 2: 1 by volume. The sample is immersed cyclically in each of the solutions by 0.5 s for 20. times; washed with running cold water and dried. The beginning and end of the treatment is carried out in hydrogen peroxide in order to passivate the surface. The microstructure clearly shows the chains of dislocation exits, sub1 fragments, tables

Way

20 40

Not detected

60

10-20

The reliefs of the surface of the specified dimensions were etched, the phase boundaries are blurred, uneven, intermittent

Nice grains. The dispersion of the detected fine structure elements is in the order of 0.1 µm.

  - #

Example 2. For preparation

55 titanium alloy for the study of structures1Hl carried out the grinding of the surface on a microfiche M 14. A mixture of hydrofluoric and nitric acids is taken in a ratio of 3; 1. The number of cycles 60 is 5, the time of immersion in each solution. - 3 s. In addition to the usual phase boundaries, a block structure of the eL phase has been detected. The dispersion of the detected structure elements is approximately

65 1 microns.

Example 3. For a sample of zirconium alloy, a mixture of hydrofluoric acid and nitric acid is taken in a ratio of 2.5: 1, the number of cycles is 15, the time of immersion in each solution is 0.5 s. The steps of growth in the yield of screw dislocations with a height of approximately 0.1 μm are revealed.

The use of the proposed method allows to simplify the process of preparing easily penetrating metals and alloys for studying their structure by eliminating a number of operations for preparing thin sections (pressing in, repeated grinding, etching) and avoiding blockages on them, drastically increasing the productivity of surface preparation for the study of structure hundreds of times in comparison with the preparation of thin sections mechanically), to prepare for the study of the structure of large-sized basal surfaces of sheets, batyvat complicated surface configuration to receive information simultaneously and on the fine structure legkopassivyruyuschihs metals and alloys, which is possible when vzrugih methods for surface preparation -Studies structure. .

Claims (2)

1. The method of preparing the surface of easily digestible metals and alloys for the study of their structure, including mechanical grinding and chemical polishing, characterized in that, in order to reveal micro, sub and fine structures with dispersity up to 0.1 µm, chemical polishing is carried out by alternately repeated immersion of the sample in concentrated solutions, first of hydrogen peroxide, and then mixtures of hydrofluoric and nitric acids, taken in the ratio (2g-3): 1, with an aging time ki 0.5-3.0 s. 2. The method according to claim 1, starting with the fact that the sample is alternately immersed in a solution 3 to 30 times. Sources of information taken into account in the examination 1.Panchenko E.V., Skakov Y.A. 5 Popov, K.V., Krimer, BI, Arsentiev, P.Ili., Ziling, M.Ya., Laboratory of Metallography .... M., Mets1Llurgi, 1965, pp.13-23. 2. McVillan A.D., McVillan M.K. Titanium. M.,. Metallurgists, 1958, p.448.