Molybdenum is a refractory metal, which has the characteristics of high melting point, high temperature strength, good thermal conductivity and electrical conductivity, low thermal expansion coefficient, resistance to corrosion by molten salts and liquid light metals. Molybdenum and its alloys are commonly used in powder metallurgy processes. Molybdenum powders doped with specific elements and compounds can be pressed and sintered to form high-strength metal products.

01Equipment and consumables

02 Sample preparation procedure

1-Mounting

After ultrasonic cleaning of the specimens, hot mounting the specimen with FlexPRESS mounting press.

FlexPRESS mounting press

2- Grinding

Polish the specimen with Alpha -600 automatic grinder&polisher, diamond grinding disc P120→P1500.

Alpha-600 automatic grinder&polisher

Diamond grinding disc

3.1-Polishing(plane polishing)

Polish the specimen with Alpha-600 automatic grinder&polisher,use YS polishing cloth with 3μm polycrystalline diamond suspension for plane polishing. Note that PL-W polishing lubricant should be added for polishing.

YS-JP white fiber polishing cloth

Diamond suspension

3.2-polishing(fine polishing)

Polish the specimen with Alpha-600 automatic grinder&polisher,use ZN polishing cloth with 0.05μm non-crystallizing silica suspension for fine polishing.(add 3% hydrogen peroxide in non-crystallizing silica suspension)

ZN-ZP black polyurethane polishing cloth

Non-crystallizing silica suspension

4- Corrosion

After 10min polishing with non-crystallizing silica suspension, The general outline of each phase in the sample has been revealed (see the figure below),Just need to corrode a little.

After polishing with silica 500×

The boundaries are clearly visible

5-Observation

03 Analysis

Mo-TiC 500×

Visible light blue TiC, black holes, white molybdenum and other equiaxed grains

Mo is a hard and tough metal. In this example, Mo and TiC are sintered, and the hardness of TiC is about 3400HV, which is much higher than 2550HV of SiC. Therefore, SiC sandpaper should not be used for grinding this metal. It should be replaced with diamond grinding disc.

Plane polishing is relatively simple, use a hard woven cloth with polycrystalline diamond suspension.

During fine polishing, use a soft damped polishing cloth for chemical mechanical polishing to release the stress on the surface of the sample, and pay attention to controlling the time to avoid too much embossing for phases with different hardnesses.

After silica polishing, since the stress on the surface of the sample is released to a large extent, the subsequent etching becomes extremely simple, and the etchant can be used to slightly rub for a few seconds. Pay attention to protection, the corrosive liquid is poisonous!

In the metallographic phase, the light blue is TiC, the black is the hole, and the white is the molybdenum equiaxed grain. The dark area around TiC should be the diffusion and fusion area of TiC and Mo.