Making Cermet II Materials

What follows are some explanations of how to make advanced carbide.  These are pretty short explanations but they will give an idea of all that is possible. 

Obviously we use different techniques for different grades and applications.  We have compiled a great deal of infomation on Carbide and Advanced Materials in our Tool Tipping Index.  

How It Works 

Carbide wear is due to micro-fracturing, macro-fracturing, grain pull out, corrosion of the binder, adhesion between the carbide and the material being cut, and tribological functions which are similar to a naturally occurring electro-etching. 

Cermet II technology uses a variety of carbides such a titanium carbide, tungsten carbide, Tantalum carbide, Niobium carbide and others.  Steel is iron with a very small amount of carbide but it is very different than plain iron.  The addition of a very small amount of the right material can make a huge difference in carbide performance as well. 

Cermet II grades also use unique binder formulations.  Cobalt is a good binder material and is used in standard grades.  It was the first binder used and is still easiest to use.  However cobalt is pure metal and is subject to chemical attack.  Part of the secret of our Cermet II grades is to chemically alloy special binders with a proprietary metalloid which makes the cobalt binder non-reactive so it doesn’t corrode.  It also greatly strengthens the binder so grinds aren’t pulled out. 

Cermet II grades have special binder properties so that they behave more as a solid piece of material than as a cemented piece of material.  Think of a steel alloy as compared to concrete.  

Grain Size 

The most important reason for this widening of the spectrum of available WC grades is that, besides those variations achieved by cobalt contents and some carbide additives, the properties of WC-Co hardmetals such as hardness, toughness, strength, modulus of elasticity, abrasion resistance and thermal conductivity can be widely varied by means of the WC grain size. While the spectrum of available WC grain sizes ranged from 2.0 to 5.0 µm in the early days of the hardmetal industry in the mid 1920’s, the grain sizes of WC powders now used in hardmetals range from 0.15 µm to 50 µm, or even 150 µm for some very special applications.  

Grain Size 

The history of tungsten carbide powder metallurgy, and especially that of the hardmetal industry, is characterized by a steadily widening range of available grain sizes for processing in the industry; while, at the same time, the grain size distribution for each grade of WC powder became narrower and narrower. 

The most important reason for this widening of the spectrum of available WC grades is that, besides those variations achieved by cobalt contents and some carbide additives, the properties of WC-Co hardmetals such as hardness, toughness, strength, abrasion resistance and thermal conductivity can be widely varied by means of the WC grain size. While the spectrum of available WC grain sizes ranged from 2.0 to 5.0 µm in the early days of the hardmetal industry in the mid 1920’s, the grain sizes of WC powders now used in hardmetals range from 0.5 µm to 50 µm, or even 150 µm for some very special applications. 

The first submicron hardmetals were launched on the market in the late 1970s and, since this time, the micro-structures of such hardmetals have become finer and finer. The main interest in hardmetals with such finer grain sizes derives from the understanding that hardness and wear resistance increase with decreasing WC grain size. 

With optimum grade selection, sub micron grain size tungsten carbide can be sharpened to a razor edge without the inherent brittleness frequently associated with conventional carbide. Although not as shock-resistant as steel, carbide is extremely wear-resistant, with hardness equivalent to Rc 75-80. Blade life of at least 50X conventional blade steels can be expected if chipping and breakage is avoided. 

Advanced Manufacturing Techniques 

Better, cleaner powder has been achieved through improved solvent extraction in tungsten chemistry as well as new techniques in hydrogen reduction and carburization to improve the purity and uniformity of tungsten and tungsten carbide powder. 

New powder milling, spray drying and sintering techniques have resulted in improved hardmetal properties and performance. Notably, the continuous improvement of vacuum sintering technology and, starting from the late 1980’s, hot isostatic pressure sintering (SinterHIP) led to new standards in hardmetal quality. 

Carbide Grain Sizes  

Sub - Micron and Nano-grain Materials

A sub-micron grain size.  This compares to ordinary carbide about like BB’s compare to golf balls.  As an example compare 0.5 microns for a sub-micron grade with 5 microns for a coarse grade.  (A BB is 0.177” and a golf ball is 1.68”) 

Neither one packs perfectly but the BB’s pack a lot closer together simply because they are smaller. 

These are balls in plastic boxes.  If you look at the corners you can see why the sub-micron grains take and hold a tighter edge.   Remember the spaces between the grains are filled with a relatively soft metal binder that is susceptible to corrosion.  You need some metal binder or the carbide part would be too brittle. 

Superior Wear (Abrasion) 

Abrasion or straight carbide wear is countered by smaller, more consistent grain size.   What is called abrasion is often thought of a straight wear. However a big part of it is actually pulling carbide grains out of the metal matrix. Smaller grains have less surface area for wear and less surface area exposed so are also less likely to be pulled out. Grains can also be more tightly packed. Both methods reduce grain exposure and loss. 

Superior Wear (Adhesion and Diffusion Resistance (corrosion and chemical attack) 

The materials used in tungsten carbide have an affinity to the materials being cut. This functions two ways. One way is adhesion where the material being cut actually sticks to the tungsten carbide in a sort of welding process. The second way is where the material being cut dissolves one or more of the materials in the tungsten carbide. Usually it is the cobalt binder, in the tungsten carbide. This is very readily seen cutting high acid woods.   Super C grade of carbide has an extremely fine structure so there is very little binder presented to the material being cut. This, combined with the special metallurgical formulation the Super C binder (hint - it’s not just plain Cobalt) 

Vickers Hardness (HV) 

Conventional l220 Kg/mm2 

Nano-structured 2260 Kg/mm2 

Cermet II – Sawmill and General Purpose Grade

(Tougher than C1  - Better wear than C4)  

Cermet II 

 Hardness (HRA)          T.R.S. (psi)  

             92.3                 537,000 

Typical C2 Values 

             Hardness (HRA)         T.R.S. (psi) 

Mfg. 1             92.1                 334,000 

Mfg. 2             91.8                 334,000 

Mfg. 3             91.5                 377,000 

Mfg. 4             90.4                 435,000 

Typical C Values 

                     Hardness (HRA)         T.R.S. (psi) 

C1                   89 - 92.4          350,000 - 360,000 

C2                   91.2 - 92.9       250,000 - 400,000 

C3                   91.4 - 93.6       270,000 - 350,000 

C4                   89.6 - 93          260,000 - 450,000 

Monolithic binders – somewhat like rebars in concrete

Grinds like regular carbide

It is tougher than regular carbide grades. Up to 30% tougher

More corrosion resistant than regular carbide grades, 475% better in Hydrochloric Acid

Stays sharper much longer than regular carbide grades

100+% better in 45-pound, double-and single-sided, vinyl laminated particleboard

20% - 30% better in hard aggregate

100% better in green oak

Why Cermet II Works Better Than Carbide 

Cermet II grade tungsten carbide is ordinary tungsten carbide enhanced with boron using advanced cermet technology.  Boron carbide is much harder and much more wear resistant than tungsten carbide.  However it is very brittle and breaks easily.  It is very good for sandblast nozzles but very bad for saw teeth. 

As an experiment boron was added to tungsten carbide during the sintering.  Two things happened.  The carbide is much more wear resistant and the carbide is much tougher.  The boron creates an intermediate compound of tungsten, carbon, boron and cobalt.  This third phase (besides cobalt and tungsten carbide) acts like rebar in concrete. 

Special Carbide Additives 

The chemistry of advanced grades is considerably different.  The standard was tungsten carbide grains cemented with a cobalt binder.  This was the first one used because it was the first one that worked.   Advanced grades vary somewhere from the traditional formula all the way up to Titanium Carbonitride with a Nickel / Chrome binder.   The advanced materials provide sensational wear properties especially in areas of chemical attack such as green lumber and MDF as well as other man made materials. 

Straight Tungsten Carbide Grades contain the highest resistance to abrasion (flank wear) of any carbide grades and have the greatest strength. The grain size and cobalt content affect the hardness, abrasion resistance and strength of the tool. Additions of other carbides reduce the strength and abrasion resistance. 

High Tantalum (28%) has very high red hardness and high.  It is excellent for removing flash from weld. 

Tantalum Carbide (TaC) and Tantalum Niobium Carbide (TaNbC) are frequently used to maintain structure edge strength at high temperatures.  In addition, TaC can be used as a grain growth inhibitor preventing the formation of large grains and increasing the hardness of the sintered part. 

High Titanium carbides with nickel as the binder have high red hardness and good wear qualities. They machine steel in the very high speed ranges, providing good surface finishes and size control. They have low strength values and are recommended for light cuts only. 

Titanium Carbide gives "lubricity" to the carbide so that the chip slides across the face of the cutter with less heat and friction. Titanium carbide additives permit the carbide to maintain high hardness at elevated temperatures. However, the more titanium carbide added, the weaker the tool is. Where the material being machined tends to crater, bind, seize, or gall the workpiece, titanium carbide bearing grades should be used. 

Titanium Carbide and Tantalum (or Columbium) Carbide resists cratering, seizing, and galling.  They resist deformation of the carbide under heavy load where very high temperatures are created. Although additions of tantalum carbide reduce the strength of the carbide, they do not reduce the strength as directly as titanium carbide additives do. Tantalum carbide maintains its hardness and strength at elevated temperatures better than titanium carbide or tungsten carbide. 

Molybdenum carbide acts as very efficient catalysts for water gas shift and reforming applications. 

Vanadium carbide is chemically stable and has excellent high-temperature properties. It can be used as an additive to tungsten carbide to make finer carbide crystals and improve the property of the material. 

Electrochemical Effects 

Electrical Conductivity - Tungsten carbide is in the same range as tool steel and carbon steel while Cermet II grades conduct more like glass. 

History 

By the addition of titanium carbide and tantalum carbide, the high temperature wear resistance, the hot hardness and the oxidation stability of hardmetals have been considerably improved, and the WC-TiC-(Ta,Nb)C-Co hardmetals are excellent cutting tools for the machining of steel. Compared to high speed steel, the cutting speed increased from 25 to 50 m/min to 250 m/min for turning and milling of steel, which revolutionized productivity in many industries. 

Specifying a large WC particle size and a high percentage of Cobalt will yield a highly shock resistant (and high impact strength) part. The finer the WC grain size (and therefore the more WC surface area that has to be coated with Cobalt) and the less Cobalt used, the harder and more wear-resistant the resulting part will become. To get the best performance from carbide as a blade material, it is important to avoid premature edge failures caused by chipping or breakage, while simultaneously assuring optimum wear resistance. 

As a practical matter, the production of extremely sharp, acutely angled cutting edges dictates that a fine grained carbide be used in blade applications (in order to prevent large nicks and rough edges). Given the use of carbide which has an average grain size of 1 micron or less, carbide blade performance therefore becomes largely influenced by the % of Cobalt and the edge geometry specified. Cutting applications that involve moderate to high shock loads are best dealt with by specifying 12-15 percent Cobalt and edge geometry having an included edge angle of about 40º. Applications that involve lighter loads and place a premium on long blade life are good candidates for carbide that contains 6-9 percent cobalt and has an included edge angle in the range of 30-35º.