Thermal Spray Metallographic Sample Mount Variables

Metallurgical quality control of thermal spray coatings is an important step for any applicator of this family of coatings because unacceptable structure can lead to premature failure. More importantly, spelled hard coatings can lead to secondary damage in critical aerospace applications and as a limiting case in the situation where there is a single engine aircraft as in most military vehicles, failure of the engine can lead to mission failure and even fatalities.

Metallurgical laboratory evaluation of thermal sprayed coatings includes but is not limited to metallographic examination of the sample. Additional tests such as erosion testing, hardness testing, tensile testing, etc may form part of the overall quality control process. While this could be the subject of an entire treatise, we will limit ourselves in this brief article to metallographic examination and in particular to the variables involved in the preparation of the mount itself.

For those that are not familiar in the art, successful metallographic evaluation begins with the preparation of a good quality mount. There are several variables involved in this step as discussed in what follows. The first and foremost variable is in the choice of the mount material itself. Bakelite is a commonly used material. Two-part epoxy compounds are also utilized by many metallurgists. To provide added strength, fine aluminum oxide powder is sometimes added to two-part epoxy compounds. For quick evaluations, hard mounts made of metal are also utilized in the industry.

When utilizing Bakelite as the material, one needs to control the variables of pressure, temperature and time of pressing to reproduce high quality mounts time and again. When two-part epoxy compounds are used, the mixing proportion of the two parts need to be controlled as well as the amount of hardening additives such as aluminum oxide need to be controlled. Mixing time and subsequent hardening time are also variables in the process.

The choice of metal used in the quick mount method is very critical. It is important that the metal be sufficiently hard so smearing of it does not occur during the subsequent grinding and polishing steps. Sometimes hard metal strips can be used juxtaposed to the coating surface during the mounting process for proper edge retention. In such cases, alteration of the edge retention material could producing varying effects during subsequent sample preparation processes.

As one can see, there are several variables even in the sample mount preparation process which if not controlled can lead to erroneous interpretation of coating quality. The best practice to avoid pitfalls and ensure consistent repeatable quality is to document the controlling practice of all these as part of the laboratory manual.

For more information about WC-12Co,Cbn Inserts,Thermal Spray Powder and Hardfacing Materials please visit my website.  

Turning Recycled Tungsten Carbide Into Tungsten Carbide Blades

Tungsten carbide is an extremely valuable alloy that is used in many industries for different applications. It is also a highly prized alloy because it can be 100% recycled over and over again. Because of its strength, durability, and resistance to both heat and rust, carbide is an ideal choice for surgical instruments, mining and drilling inserts, jewelry, and grips for all sorts of sporting equipment. However, another widespread uses for carbide, especially after it has been recycled, is to make cutting blades with it.

Tungsten carbide is an ideal material to forge blades out of because thanks to its hardness and other properties, a much finer yet more durable edge can be fashioned once the blade has been formed. Carbide blades need far less sharpening than those made of stainless steel or titanium. Moreover, they will not pit, corrode, or break under normal wear and tear.

Why Recycled Material is Used for Blades

The most prominent reason why it makes sense to use recycled carbide for fashioning cutting blades is because of the lack of material that is available domestically. Roughly 90% of all tungsten is mined outside of the United States and since it takes both tungsten and carbon to create tungsten carbide, domestic producers are forced to either import material from overseas or search for recycled sources stateside. Using recycled carbide is the only way to create a viable domestic market for the product and this is why tungsten carbide recycling companies will typically pay between $7 and $11 per pound for scrap that would otherwise be thrown away.

How Carbide Blades are Made

There are many types of blades that utilize tungsten carbide such as rotary saw and planning blades, scalpels, and hunting or fishing knives. There are two ways that any of these tungsten carbide blades can be made. The first way involves creating the blade from 100% tungsten carbide. To do this, the recycled material is melted down, molded, and forged if necessary into the shape of the blade. After the basic shape is in place, it is grinded to perfection, polished, and given its edge. Unfortunately, this is not always the best way to use carbide to make a cutting blade.

Tungsten carbide's incredible hardness (second only to diamond) can actually become its downfall here. This is because the material's atomic structure is woven so tightly together that regardless of what shape it takes, it has no give whatsoever. Whereas stainless steel, titanium, or aluminum blades can bend when under pressure, carbide will actually shatter much like glass. This means that if you were to try and put too much pressure on the blade or even drop it on a hard surface such as tile, the force against the blade from heavy pressure or an impact could destroy it entirely.

To combat this problem, blades using the benefits of tungsten carbide can be made a second way that involves a more practical grafting process. To do this, the base and main structure of the blade is created out of another material with high strength, but more give such as stainless steel or titanium. Only the blade's edge is made of carbide. 

For more information about Hardfacing Materials,Thermal Spray Powder China,Cbn Inserts China and Cast Tugnsten Carbide China please visit my website.