Titanium alloy forging grinding technology

1. Difficulties in grinding and polishing titanium alloys
The preparation of metallographic samples of titanium and titanium alloys is more difficult than that of steel. Its grinding and polishing efficiency is low. Excessive cutting and polishing processes will produce deformation twins in the α phase. After deformation twins are generated, the microstructure of titanium will change. Analysis will be disrupted.
Cold mounting of pure titanium is more suitable than hot pressure mounting. Hot pressure mounting may change the content and distribution of hydrogen in pure titanium. It is very difficult to remove scratches and plastic rheology from pure titanium during sample preparation.
2. Introduction to the metallographic characteristics of titanium and titanium alloys
Titanium and titanium alloys have been commercially used for more than 50 years. They have the advantages of low density, excellent strength to weight ratio, good corrosion resistance and high mechanical strength. The disadvantage is that titanium and titanium alloys are very expensive to produce.
Titanium, like iron, has an allotropic transformation. Like steel, titanium can also be heat treated, and alloying elements have a certain influence on the stability of the low-temperature α phase and the high-temperature β phase.
At room temperature, the stable phases of titanium and titanium alloys exist as alloy-containing α, α-β and β phases. The other two phases are: near α and near β phases.
3. Development of titanium alloy polishing technology
In the early days, the mechanical polishing process was quite time-consuming, and almost all mechanical polishing methods used polishing solutions containing erosive agents in the last step or two polishing steps.
The electrolytic polishing method can often obtain a better polished surface, but there are certain dangers in the electrolytic solution during the electrolytic polishing process. These electrolytic solutions also have some chemical polishing effects.
In the 1970s and 1980s, the mechanical polishing method of titanium and titanium alloys still continued the old polishing method. Springer and Ahmed first published an article on the polishing method of titanium and titanium alloys in 1984.
This is the three-step sample polishing method, assuming that 320grit sandpaper is used to complete the sample grinding process, but this may not always be the case. If an ultra-thin cutting disc or a grinding wheel cutting disc with suitable bonding strength is used when cutting the sample, the cutting surface is smooth and the damage layer is minimal, then 320grit sandpaper can be used to complete the grinding process of the sample. If the surface after cutting is rough and the damage layer is large. For example, cutting with a band saw may produce such results. In this case, you must use coarser sandpaper and spend a certain amount of time to remove the damaged layer.

4. Springer and Ahmed titanium alloy three-step polishing technology
1) Grind smooth, use 320grit sandpaper to cool with water, and grind for 2 to 3 minutes to remove the damage layer caused by cutting and make the surface of the sample flat. Use 320gritSiC sandpaper, water-cooled, rotating speed 240RPM, rotating in the same direction*, pressure: 27N (6lbs)/each sample until the sample is ground smooth.
Note: Removing the cutting damage layer is the basic task of polishing. If it is not removed completely, the direct consequence is that the observed phenomenon may be an artifact.
2) For rough polishing, apply 9μm metaDI? diamond polishing paste on the holed TEXMET? polishing cloth in advance, use distilled water as cooling lubricant, and polish for 10 to 15 minutes. Rough polishing process: 9μmmetaDI diamond polishing fluid + metaDI polishing lubricant, using ULTRA-PAD? polishing surface, speed 120RPM, reverse rotation**, pressure: 27N (6lbs)/each sample, time 10min.
3) For final polishing, use MICROCLOTH? or MASTERTEX? polishing cloth, add MASTERMET? silica suspension polishing liquid, and polish for 10 to 15 minutes. Final polishing process: Use MASTERMET silica polishing fluid on the MICROCLOTH polished surface, rotating speed 120RPM, reverse rotation, pressure: 27N (6lbs)/each sample, time 10min.
Note: During the polishing process, the sample needs to be rotated regularly. There is a hard phase in most metal alloys. If the direction is not rotated, the polished sample will have a black "long tail" on the hard phase, which affects the metallographic quality. Solve The key to the "long tail" problem lies in the direction in which the sample is turned. It can be rotated 90 degrees or 180 degrees each time.
5. Müller titanium alloy three-step polishing technology
1) P500 sandpaper is water-cooled, the rotation speed is 300rpm, the pressure on each sample is 16.7N (3.75lb), and the preparation time is until all samples are smoothed.
2) P1200 sandpaper is water-cooled, the rotation speed is 300RPM, the pressure on each sample is 16.7N (3.75lb), and the preparation time is 30S.
Note: The specific time is determined by personal polishing conditions. The time parameter is only a reference. Usually manual polishing is used. There is no such advanced equipment, so the parameters will be different.
3) Use synthetic lint-free polishing cloth + silica suspension polishing liquid containing chemical corrosives, polishing machine speed 150RPM, polishing time: pressure on each sample is 33N (7.5lb) for 10 minutes, pressure on each sample is 16.7N ( 3.75lb) for 2 minutes and a pressure of 8N (2lb) on each sample for 1 minute.
4) Polishing agent ingredients: 260mlSiO2+40mlH2O2 (concentration 30%), 1mlHNO3+0.5mLHF. FEPA standard P500 and P1200 sandpaper grits correspond to ANSI/CAMI standard 320/360 and 600grit sandpaper respectively.
6. The difference between manual polishing and machine polishing
1) Manual polishing requires experience. The strength of the hands, time, and rotation speed all require experience and long-term work to master these key parameters, while machine polishing only requires setting the parameters. For novices, they are often impatient and have problems such as under-polishing or over-polishing.
2) The principles of machine polishing and manual polishing are the same. Most metallographic work in China is still dominated by manual polishing. Manual polishing requires a lot of patience from the metallographic staff. Over-polishing requires repeated polishing. However, as long as you have patience, try more and summarize, you can also obtain good metallographic polishing. Therefore, it is necessary to carefully sum up experience, and sweat will eventually be rewarded.