Elaboration and Tribological study of WC-35 wt%(Fe-Co-NI)hard metal alloys obtained by liquid
phase sintering
Fares Djematene , Boubakeur Djerdjar Laboratoire Science, Génie Matériaux (LSGM) Université Houari Boumediene Alger, PB 32 El Alia 16111,
Bab Ezzouar 16111, Algérie.
Ali Mameri
Laboratoire Elaboration, Caractérisation des Matériaux et Modélisation (LEC2M)
Université Mouloud MAMMERI de Tizi-Ouzou, PB 17 Hasnaoua 15000, Algérie
Abstract— this study concerns on the mechanical behavior (friction wear) of WC-35wt% (Fe-Ni-Co) hard alloy. The alloy was prepared by liquid phase sintering process with a temperature of 1350 ° C under argon. Haw ever This alloy is working under severe conditions of wear and friction. have undergo a series of dry friction tests involving multiple parameters. Interesting results have been obtained (good wear resistance and a stabilization of the friction coefficients). The wear rate (mm3 / m) increases with increasing of the applied load 5N and 10N, these results open up broad prospects for their jobs in the petrochemical fields (drilling tools, turbine parts).
Keywords—friction, WC, phase, alloys, sintering, wear
I. INTRODUCTION
Development of new products of modern industry tribological properties are becoming increasingly important, the tribological research includes the application of the principles of friction, wear and lubrication[6].The excellent resistance of tungsten carbide combined with its high hardness is an important factor for efficient production. His use is particularly recommended for all mechanical components against wear and friction mandrels and drawing dies, tools for metal packaging, stamping tools and cold forming, sandblasting nozzle, powder compression tools, cutting tools.
[1]
The goal through this work is to determine the mechanical characteristics (behavior study to chafing dry and resistance to deformation) under certain conditions of the alloy, we have developed by liquid phase sintering from a 35wt% based matrix (Fe, Ni, Co) and a reinforcement based 65wt% WC.
Many studies have focused on the wear behavior of and alloys. Shih-Hsien Chang et al concluded that the WC-Co-Fe- Ni alloy showed better hardness and abrasion resistance
compared to that of WC-Co, [1] this is due the influence of small particle size iron and nickel and their high modulus of rigidity. [2]
This research focuses on a tribological study of an alloy containing WC-35wt% (Fe-Ni-Co) alloy is produced by the sintering method in a controlled atmosphere (argon). The tribological tests are performed dry with a sliding configuration Bille-disc, in our case the ball is alumina and the disc is our alloy. [4]The objective of this work is to focus on the evaluation of the effect of the load on friction and wear of the WC-35 wt% (Fe-Co-NI) alloy.
II. EXPERIMENTAL METHOD A)- PREPARATION:
tungsten carbide (10 mm, 99% purity by BMI group. Martec, France), nickel (2 mm, 99% purity by Sulzer Metco, France), iron (1 mm, 99.8% purity , Aldrich, France), cobalt (1.6 mm, 99.8% purity, Alfa Aesar, France), were used as raw materials.
The composition are given in Table 1 :
TABLEI. THE MASS CONCENTRATIONS OF ALLOY NUANCE.
Elements Fe(wt. %) Co(wt. %) Ni(wt. %) WC(wt. %)
percentages 15 10 10 65
In this work, the raw powders of WC-Fe-Co-Ni were mixed at room temperature in a 3D mixer for 1 hour to ensure a uniform distribution and a better lubrication of the particles of the powder. [7]Respectively, during the forming process, the powders were placed in a hardened steel mold (z200), and
a vertical force of a hydraulic press was applied to the mold at a pressure of 250 MPa, which was maintained for 5 min. the powders were then subjected to a sintering process under argon wherein the sintering temperature was 1350 ° C for 1h,
B. CARACTERISATION:
Samples phase compositions were identified by X-ray diffraction was made on the type of diffractometer SIAMENS D5000. hard alloy microstructures were examined using an environmental scanning electron microscope (JEOL JSM) equipped spectroscopy to energy dispersion (EDS).
HRA hardness testing (ROCKWELL HARDNESS A) were carried out on a brand durometer (AFFRI), with a penetrator in hard steel. The test was performed according to ASTM E92-82, under a load of 588 N, for 5 seconds on polished sections; several tests were performed to obtain the average value WC-Fe-Co-Ni hardness. The surface roughness was calculated using a brand roughness TR100.
Dry sliding tribological tests were carried out on a tribometer TRB WSC ball configuration to disk in rotation, according to ASTM G99 -95 [8].
In this case, the ball of static partner (counterparty) was an alumina ball having a diameter of 6 mm. Dry friction was carried out at room temperature over a period of 69 min, in distance of 1000 m and a humidity of 40 %. The linear velocity is 10cm/s and the angular velocity is 400 tour/min, normal loads ranged from 5N and 10N, the rotation diameters are 4.5mm and 3.5mm.
The sample volume loss is given by the following equation:
Vdisk= 2πR [r2sin-1(d⁄2r)-(d⁄4)(4r2-d2) (1⁄2)].
With R: ray of wear track.
d: width of the wear track (1) r: radius of the ball
The wear rate is given by the following formula:
Ws=Vdisque⁄ DS FN (2)
With : Ds: distance traveled.
FN: Normal strength.
The radius of the track wear is calculated from the micrograph images obtained by light microscopy (Nikon) at magnification 50 X using conventional metallographic techniques. Four measurements were taken per sample at different positions in the groove[9].
III. RESULTS AND DISCUSSION:
A. The hardness and roughness:
The test result of the HRA hardness of the alloy = 65.96.
This slight decrease can be explained is by the great content of the binder phase and the influence of the ductile part 35wt%
(Fe, Co, Ni) of the material, which slightly reduces the hardness of the material surface. The roughness after polishing our alloy and 0.697 ± 0.085 microns. [3].
B. Composition and microstructure:
Fig. 6 shows the EDS analysis of the alloy, to identify and quantify its composition. It revealed the presence of a major phase of tungsten carbide WC, and the presence of binder consisting of Fe-Co-Ni. Figure shows the presence of a certain porosity and the distribution of elements is homogeneous it is due to good mixing of powder.
Fig. 1. SEM micrograph of WC-35 wt% (Fe-Ni-Co) alloy and EDS analysis result
C. tribological behavior : 1) Coefficient of friction :
The two measurement curves of the friction coefficient of the WC-35 wt% (Fe-Co-NI) alloy against the alumina ball as the two loads 5N and 10N with an angular speed of 400 rev / min is given in Fig.2:
5 N 10 N
a c
b
b c
a
Fig. 2. Evolution of the friction coefficient in function of the distance (1000 m) under two different loads (5N and 10N).
The values of the friction coefficient for the two loads increase with time to a certain value, then stabilized at a mean value of dynamic friction coefficient [10]. The friction coefficients are of the order of 0.25 and 0.17 µm for the WC-Fe-Co-Ni under a load of 5N and 10N, respectively. In remarks that the increase of the applied load leads to decreased coefficient of friction, this can be explained by the fact that the area of the contact surface is larger when increasing the applied normal load and subsequently promote the appearance of the third body which facilitates the sliding of the ball on the alloy[12].
In general, the friction coefficient decreases significantly with increasing load; the ball compresses the material by pushing the sides to form beads, which facilitates its movement. In contrast to a small force, the material passes below advantage of the ball [6].
The time of stabilization of the friction coefficient represented by the first part of slope (convenience time) decreases with the load applied this is explained by the increase of the contact surface with the applied pressure, allowing a deformation plastic sharper bumps and faster accommodation [10].
2) wear rate :
The variation of the wear rate (mm3 / m) based on normal 5N and 10N expense is presented as a histogram in fig.3, The wear rate increases proportionally with the increase of the applied normal load, it is observed that the wear resistance of the WCwt%-(Fe, Co, Ni) alloy drop depending on the load.
Indeed, the experimental results have shown that the wear rate is rather dependent on the experimental parameters as the normal force. And detachment of the powders gives rise to cavities in the contact surface which are at the origin of the increased roughness[9]. This roughness increases the sliding resistance, which has the effect of increasing the tangential force and subsequently the coefficient of friction. This image provides a good correlation to the wear curves [4].
Fig. 3. Evolution of the wear rate as a function of the load (5N, 10N) for WC-Fe-Co-Ni at a speed of 400 rev / min and a distance of 1000m The fig.4, shows deference to the width of the groove between the load and 5N 10N.la groove width for the load of 5N = 0.17327 mm, and the load of 10N = 0.29904, in remarks that there is a relationship between the groove width and the rate of wear. Small entangled stripes spread across the worn surface.
Level analysis of wear tracks show a disturbed morphology.
They also prove the existence of abrasion and two to three body and the predominance of one to two bodies [7].
Fig. 4. Evolution of the wear rate as a function of the load (5N, 10N) for WC-Fe-Co-Ni at a speed of 400 rev / min and a distance of 1000m
IV. CONCLUSION:
The objective of this work was to study the tribological behavior of the alloy based on tungsten carbides in a matrix of Fe-Co-Ni, in particular, the correlation between a development parameter (binder composition , sintering temperature) and the wear resistance. Through this study, several points are clear :
The Optical micrographs of the sintered pellets show a homogeneous distribution of the elements constituting the composite. This allows us to consider that the operating conditions were adequate mixing.
The SEM micrographs in backscattered electrons have revealed the formation of areas of connections called solder bridges within the matrix that is the flow of material between the grains, which led to this training, thus, the sintering parameters (temperatures and time) were chosen favored consolidation mechanisms.
The wear tests conducted on the samples formed by the matrix reinforced by tungsten carbides have shown high
Piste d’usure 5 N
Piste d’usure 10 N
Piste d’usure 10 N Piste d’usure
5 N
a
b
resistance to wear, always because of the resistance of the binder that contains tungsten carbides.
The results of the study of the influence of the load (respectively 2N and 5N) on the rate and wear coefficient performed on the alloy WC-Co-Fe-Ni. Show an increase in the wear rate under a load of 10N compared to 5N, which seems logical and expected.
The wear rate is much more important than the worn track of the sample is low in WC, explained that the WC particles have good resistance to wear.
The studied composites wear mechanism is mixed, between abrasion and adhesion. However, abrasive wear is the dominant mechanism.
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