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Experimental Study
In highly abrasive wear strains metal-matrixcomposites
(MMC) have proven of value, because of their
characteristics. They combine advantages of a tough
matrix, based on nickel, cobalt or iron, together with hard
material that protects against wear like carbide, boride and
nitride. As a proactive-oriented method the samples were
produced with plasma transferred arc welding (PTA), since
this method can cost-effectively achieve layer depths of 2
to 3 mm in one layer. Another advantage of the PTA method
is a highly controllable energy input, which helps achieving
very low degrees of mixing of a few percent.
Table. 1:
Type, size and chemical composition of
the used carbides
Issue 04 | 2010
TRANSFER OF TECHNOLOGY
Pic. 5:
Wear patterns of purely abrasive (left) and combined hitting/jabbing and abrasive
(right) strain
Type
Cconcentration
Various tungsten carbides were used for the tests, in
combination with a commercially available NiBSi-alloy as
matrix material. Broken mono crystalline tungsten carbide,
broken Fused Tungsten Carbide (FTC) und spheric Fused
Tungsten Carbide (SFTC), Tab 1. Beside the type of the
influence of the carbon concentration and the grain size
of the carbide on the wear opposition was also analysed.
The mixing ratio of hard material to matrix powder of 60
to 40 mass percent was held constant for all tests like the
welding parametres, tab. 2..
In addition to the percussion wheel, three more test
benches were used, out of which two were standardized
according to ASTM. The Miller test, specified according
to ASTM G75-07, originates from the petroleum industry,
Picture 6.
Size in µm
1 WSC fractured 4,3 - 5,0 53 - 180
2 WSC fractured 3,8 - 4,2 63 - 180
3 WSC fractured 4,3 - 5,0 53 - 180
4 WSC fractured 3,8 - 4,2 100 - 150
5 WSC fractured 3,8 - 4,2 210 - 400
6 WSC fractured 6,1 63 - 180
Electric
current in A
Plasma
voltage in V
Welding speed
in mm/min
The sample is directed with a velocity of 20
m/min, oscillating in a defined suspension of
water and aluminum oxide. The down force
is 22,24 N, at a test time of six hours, which is
passed in three intervals [2].
Oscillation
width in
mm
Powder
feeding in
g/min
Table. 2:
Welding parameters
Mixing ratio
NiBSi/W(S)C
150 28 102 40 120 +/- 4 40/60
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