Making Advanced Materials

There are Saw tips that work 2, 4, 5 and 10 times as well as standard carbide grades

They braze and grind like carbide. 

Advanced Grades

Tungsten Carbide Cermet II, True Cermets, True Ceramics

Three Advanced materials

Cermet II – proven cermet grades that always work.  These are grades that have worked well in field tests for a year or more.  They have never worked worse than carbide and about 95% of those who try them are now ordering them in thousands at a time.   About twice the price of carbide and worth it as they can give results five to ten times as good.

Cermets – experimental grades of various chemistries that sometimes work and sometimes don’t.  Sometimes are much better than carbide and sometimes much worse. 

Ceramics – experimental - should work well in brazed applications as they do in mechanically held applications but they haven’t worked yet. 

Good Carbide   

Good carbide

Coarse grade left

Fine grade right

Left is poorly made carbide.  The grains are very poorly distributed.  The next two pictures show grains evenly distributed which is the ideal and it show that the grains are tightly packed.  What we do is to take the tightly packed, evenly distributed grains and add a separate chemical component that acts like rebar to take a randomly arranged, cemented structure like ordinary carbide and create a super monolithic structure with much greater resistance to both macro and micro fracturing.   

Monolithic binders – somewhat like rebars in concrete

ü      Grinds like regular carbide

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

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

ü      Stays sharper much longer than regular carbide grades 

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

Ø      20% - 30% better in hard aggregate

Ø      100% better in green oak

                                    Carbide                        Cermet II

Sawmill                        40 hrs.                          422 hrs

Copper tube                 5,408 cuts                    22,743 cuts

Fiberglass                     16 - 18 holes                24 holes

 Grain Size & Cobalt % Compared to Hardness & Toughness

In the very early days of carbide you made carbide tougher or harder by changing the amount of Cobalt in the binder.  Cobalt is metal and softer than carbide grains so more cobalt made it tougher and less made it harder. 

Toughness

Co %

Then people learned how to change the grain size.  Bigger grains made carbide tougher and smaller grains made it harder. 

Toughness

Grain size

By varying grain size and cobalt % you can make carbide a lot tougher or a lot harder. 

 Toughness

  Co %

Grain size

If you add more Cobalt to large grains then you get even more toughness.  However there is a limit to how tough you can make carbide or want to make carbide.  If you get it too “tough” then it is too soft.  Remember we are using the term ‘tough’ here as the opposite of hard. 

If the grains are too large and there is too much Cobalt then the carbide will  move and deform under pressure.  One of the major strengths of carbide is its ability to handle pressure or compressive force.   If it is too soft it loses that ability.   

             Toughness

Grain                           =

Size

                 Hardness

                   Cobalt %

What you can do is mix Cobalt % with grain sizes and get carbide that is both tough and hard so you get long wear without breakage.  

Toughness

Hardness

Co%

Above is a graph of 23 different grades of modern carbide.   You can see by the Co% line on the bottom that as co% goes up hardness drops and toughness stays sort of the same.  This is because grain size differs.

Toughness 

Hardness

Grain size

Here we increase grain size and hardness drops while toughness sort of drops. 

Toughness

Hardness

Grain size

Co %

Here you can see 23 grades.  I graphed it so that the Cobalt slowly increases.  You can see where hardness seems to relate to grain size more than Co% especially in a couple places.   You can also see a lot of places where hardness and toughness don’t seem to relate to grain size and Co % much at all.   

These graphs are confusing and that is the point. - Neither Cobalt percentage or grain size alone determines how a grade will perform. 

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. 

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.

The history of tungsten 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.

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.

Grade            size in microns     comparison

X coarse                   6  +          Weather balloon

Coarse             2.5 – 6.0            Beachball

Medium           1.3 –  2.5           Basketball

Fine                  .9 –  1.3           Softball

Sub micron        .5 -    .8            Baseball

Ultrafine           .2 -    .5             Ping Pong

Nanograin            0.2    

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 gold ball is 1.68”)

                       Front shot showing packing                             Top shot showing how spheres pack in corners

 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 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)

Typical C          Hardness          T.R.S.

Values              (HRA)              (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

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

                                    92.3                  537,000

Typical C2 values  Hardness (HRA) T.R.S. (psi)

C2                                92.1                  334,000

C2                                91.8                  334,000

C2                                91.5                  377,000

C2                                90.4                  435,000

HIPing – Hot Isostatic Pressing

                 Chance               Before         After       

                 of failure              HIP            HIP 

  Hot Isostatic Pressing takes material to a temperature just below melting.  While it is soft the HIP process uses tremendous pressure to squeeze the material evenly from all sides.  This gives a very consistent material free of all voids and gaps.  

 Corrosion Resistance & Chemical Attack

                  Beaker with 50% Nitric acid                 Tungsten Carbide                                Cermet II

We took a beaker with a 50% solution of Nitric acid and dropped carbide and cermet II saw tips into it.  You can see by the pictures that carbide reacted vigorously with the acid.  The cloud of bubbles coming off it is proof of the reaction.  The Cermet II saw tip just sat there and did not react at all. 

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.

Successful Cermet II Applications

We called customers who had ordered and re-ordered and this is what they told us they were doing.   The applications and the testimonials to success don’t mean nearly as much as the fact that they keep reordering. 

Ø      trimming to size at plywood plant, any custom blade he makes, Rip saws cutting , Pine and Fir, Panel saws cutting Melamine

Ø      running/making panel saws  for tooling industry for shelving furniture and Laminated particleboard. He was using  C-4 grade now and was looking for abrasion resistance. 

Ø      noticed improvements and keeps reordering for a customer of his who makes blades.

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