Polished hard alloy plates of TNMG 22 04 12 with multilayer wear proof coatings were used. Experiments on the hard alloy tool were carried out on steel 40X on the machine tool 16K20, at cutting speed of 310 m/min and depth of cutting 0.4mm. The feed rate was changed from 0.05 to 0.3 mm/turn.
The experiments to study the deterioration mechanism were conducted on a tribometer which is integrated with a computer for processing the data. This set-up allows us to study the tribological characteristics of materials, to investigate the process of contact interaction and also to measure the temperature at the contact zone [12]. Pictures of the cutting edges of these plates have been taken using high resolution (x800) camera.
The comparison between the friction coefficient obtained with pin-on-disc tests and that acquired in metal cutting laboratory conditions allows concluding that pin-on-disc tests, when performed with an adequate control of texture and surface roughness, are capable of providing a good estimate of the average value of the friction coefficient in metal cutting applications [13]. Tribological contact is created by pressing the motionless penetrator (finger) against a rotating disk on which the samples are kept to produce a face friction [14]. Applications of samples with the following geometrical sizes are possible in the pin on disc tester:
- "Penetrator" - the cylinder Ø3 to Ø6 mm; height of 25 mm
- Disk - Ø50 to Ø55mm and thickness 3 to 10 mm.
Loading on samples from 0.5N to 50N, the radius of friction measurement from 0 to 20 mm, speed of rotation of the disk 15rpm to 1500 rpm.
Registration of values of force of friction is transferred to the computer by means of the built in analogue-digital converter.
Influence of speed of relative sliding Vск. m/min, on friction factor μ at constant loading N=5N is studied. Speed of rotation of the disk is 55 rpm. Following are the conditions set for the tests:
1) For obtaining a factor of friction on each mode, the test continues till the reception of its stable value;
2) On each mode, three samples were tested.
The principle of action of the measuring device consists in developing a pair of friction, consisting of a motionless penetrator pressed to a rotating disk. Registration of friction force is based on measurement of deformation of a U-shaped elastic beam. An inductive converter is connected to the other end of the beam which holds the motionless penetrator. The bend of the beam under the influence of the friction force is measured using this inductive converter [15].
Coefficient of friction, is ratio of the frictional force resisting the motion of two surfaces in contact to the normal force pressing the two surfaces together. It is usually symbolized by the Greek letter mu (μ). Mathematically, μ = F/N, where F is the frictional force and N is the normal force. Because both F and N are measured in units of force (such as newtons or pounds), the coefficient of friction is dimensionless [16].
Penetrators are made of alloyed steel with coating and without coating, both of them having radius of sphere r =20mm. Disks were made of steel 45 (180 HB) and the tempered steel 45Х (50 HRC).
Chosen material for coatings are TiN, TiSiN, and ZrSiN (Table.1).
TiSiN, and ZrSiN are deposited at two different modes and compared among themselves, and also TiN coating was done for comparative study.
Table 1: Structure, mode of deposition and structural features of the investigated coatings.
Coating material
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Deposition mode of coatings: Voltage V (pressure of nitrogen 2 ,7 Pa)
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70V
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150V
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TiSiN
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columnar structured coating
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Layer by layer structured coating
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ZrSiN
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TiN
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The mode of coating corresponds to the maximum firmness of the metal-cutting tool
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