EFFECT OF HEAT TREATMENT ON ABRASIVE WEAR BEHAVIOUR OF NI-WC COATINGS
Ankit Sharma, Dr. T. K. Mishra
Gyan Ganga Institute of Technology and Sciences, Jabalpur
Abstract - In this study, the abrasive wear behaviour of HVOF-sprayed Ni-10WC metal coatings was investigated experimentally. The coating was modified with different heat treatment temperatures as 400° C, 600° C, 800° C. The porosity and hardness were investigated along with coatings and were characterized by scanning electron microscopy (SEM), Energy dispersive spectrum (EDS), and x-ray diffraction to investigate microstructure, element analysis, and phase identification. The result shows that heat treatment significantly improves the mechanical and microstructure properties of coatings.
The optimum temperature was found at 600° C and showed maximum hardness, minimum porosity and wear. Heat treatment makes microsmicro structure dense and reduces the formation of W2C phase and reduces the decomposition
Keyword: Wea, r HVOF, SEM, Coatig, XRD EDS, Hardness.
1 INTRODUCTION
Steel is a material that is frequently used in engineering applications, not only because it is readily available on the market but also because the many steel alloys and grades offer a variety of features that cannot be found in any other family of materials. The presence of carbon and other alloying elements in steel has a significant impact on microstructure alterations as well as mechanical and tribological properties. To alter the microstructure and mechanical and tribological properties of these kinds of materials, a wider array of thermal spraying techniques could be used.
The choice of material is significantly influenced by economic factors. There is therefore a need for hard material, which is the least expensive and most easily accessible. Steel is a material that is frequently utilised in engineering applications not only because it is readily available on the market but also because there are The majority of work in India is done with low- and medium-carbon steel, and as the price of steel rises owing to the inclusion of alloying elements, mild steel offers a solution because its price is so much lower than that of other alloy steel.
Only after carefully considering the part design, wear mode, material, and environmental interactions may the appropriate material be chosen.
The usual definition of wear is the unwelcome degradation of an element caused by the removal of material from its surface. By moving and separating particles from the surface, it happens.
Steel's mechanical characteristics are
drastically diminished by wear. The rubbing of metals against one another, the erosion caused by liquid and gaseous media, the removal of solid particles from the surface, and other surface processes all contribute to material wear. In laboratory studies, wear is often measured as a material's weight loss, and wear resistance is defined as the weight loss per unit area per unit time. The primary wear categories are shown below and described.
Abrasive wear
When non-metallic particles pierce the surface of a metal object, metallic debris is removed as a result. A common method of failure for engineering components is abrasive wear. With an increase in hardness, the resistance to abrasive wear generally rises[1].
Metal-to-metal wear or adhesive wear
This wear was brought on by the sliding or rolling motion of two metallic surfaces that were mated. High contact pressure results in the rubbing component's persistent plastic deformation[2].
Erosive wear
Relative movement between metal and liquid or gas causes erosive wear.
Corrosive wear,
Corrosion is the term for material degradation caused by the environment.
Surface corrosive wear develops into matrix corrosive wear over time[3].
Fatigue wear
The category of fatigue wear includes the elimination of particles by cyclic processes. In the majority of useful machines, this kind of wear is predominant.
1.2 Surface Modification by Surface Treatments and Coatings
The working environments for machine components including rolling-contact bearings, traction drives, gears, tappets, and cams include high surface temperatures, high speeds, high corrosion environments, high operating temperatures, and high loads. Pitting, a type of surface breakdown, consequently happens. itting, a type of surface breakdown, consequently happens. In addition to the different three Coating deposition techniques, such as thermal spraying, physical vapour deposition, chemical vapour deposition, and electrochemical deposition, surface hardening processing or surface treatment techniques, such as induction hardening, flame hardening, carburizing, and nitrating are applied to the machine e The rolling contact fatigue life is increased even though it is highly challenging to choose the best surface modification treatment based on the intended use.
Some approaches are utilised to reduce friction and wear. Coatings are materials that resist wear and can be categorized as hard coatings[4].
1.2.1Hard Coatings
Hard coatings are primarily used to decrease wear on heavily loaded components. Due to their innately high hardness, ferrous and nonferrous metals, ceramics, metallic alloys, and cermet coatings offer good wear resistance. These coatings can be deposited using a variety of deposition processes, including electrochemical deposition, thermal spraying, physical vapour deposition, and chemical vapour deposition. Their thicknesses range from a few micrometres to several millimetres. After hard chromium, nickel is the metal that is coated the most. Although nickel has a lower hardness than chromium, it is still an excellent heat conductor, has good mechanical strength, and is resistant to corrosion and oxidation.
Coatings of ferrous-based alloys (steels and cast irons) are used where heavy wear is met, under circumstances that impose thermal and mechanical shock.
These are applicable in wear and corrosion and resistance. Cobalt and nickel based alloy coatings are greater in hardness and wear resistance at high temperatures.
1.3 Techniques for Surface Modification
For the change of surface properties to enhance the tribological performance of machine elements, numerous coating deposition and surface treatment procedures are available. The specific surface modification technique has an impact on how well coatings and surface treatments perform in terms of load carrying capacity, wear resistance, and coefficient of friction. The functional requirements, shape, size, and metallurgy of the substrate, the availability of the coating material in the required form, the adaptability of the coating material for the technique, the desired level of adhesion, the availability of coating equipment, and cost all play a role in the choice of coating deposition or surface treatment technique. Additionally, the substrate must be compatible with the methods used for coating deposition and surface treatment.
1.4 Techniques for Coating Deposition There are several coating deposition processes available for customising surface properties for tribological applications. They are primarily split into three categories: plating, vapour deposition, and hard facing. The following is a quick explanation of various significant and well-known coating deposition techniques:
1.4.1 Hard Facing
By thermal spraying and welding, hard facing is used to instal thick coats (usually 50 m or thicker) of hard, wear- resistant materials. These procedures are briefly outlined as follows:
1.4.2 Spraying
The thermal spraying technique is currently the most adaptable and simple coating process on the market. The thermal spraying technique is providing
hard coating to the work piece with minimum thermal distortion of the material.
Thermal spraying is used when excellent wear resistance and corrosion are necessary. The feed material for thermal spray coating is heated until it melts, at which point it is launched toward the base material, which is typically water cooled. As the molten feed material particles strike the base material, the temperature of the base material rises by several hundred degrees Celsius, but it stays below 2000 degrees Celsius. The foundation material is still below 2000°C even though the molten particles striking it have a temperature of several hundred degrees Celsius. A flame created from combustion gases can generate the thermal energy required to melt the material for spraying. It is necessary to pre-roughen substrates for thermal spraying in order to improve wear and adhesion.
1.5 Thermal Spray Methods and Processes
There are several subgroups that fall under each of the three main categories of the members of the thermal spray family of processes: flame spray, electric arc spray, and plasma arc spray. (Cold spray is a more recent member of the thermal spray process family. Although some small preheating is often used, this process mostly uses kinetic energy. The article "Cold Spray Process" discusses the special qualities of cold spray. A quick assessment of some of the more commercially significant thermal spray procedures is made, along with comparisons of key procedural aspects of these methods. The following factors are often taken into account when choosing the best thermal spray technique:
• Desired coating material
• Coating performance requirements
• Economics
• Part size and portability 1.6 Heat Treatment of Coatings
Conventional coatings offer processes microstructure that directly affect the mechanical and tribological properties due to the presence of some unmelted powder and separation of carbide particles. . Heat treatment reduces the separation of carbide particle and melted
particles which remains unmelted during deposition[9].
1.7 Nickle – Nickle (Ni) increases wear and corrosion resistance. Which also act as a binder and often used with different carbide materials like silicon carbide, tungsten carbide etc.
1.8 Tungsten- Tungsten (W) offer higher wear resistance and often usen to fabricate the tool and deposited the hard material on the MS substrate. Tungsten carbide coatings are widely used in industries to increases the wear resistance and hardness of surface[10].
2. LITERATURE REVIEW
1. Jin Du et al. (2020) -On a 16Cr5Ni stainless steel substrate, WC-12Co coatings were applied using a high- velocity oxygen fuel (HVOF) technique. These coatings were then subjected to a one-hour heat- treatment in a tube furnace under a nitrogen environment at various temperatures of 650, 800, 950, and 1100 C. The effects of heat-treatment temperature on the characteristics and cavitation erosion resistance of WC-12Co coatings applied as- sprayed and after heat treatment were investigated. Ultrasonic cavitation erosion equipment was used to conduct the cavitation erosion test. The coatings' surface and cross-section morphology, porosity, microhardness, phase composition, and other characteristics were all described.
The coating that had been heat- treated at 800°C shown the best cavitation erosion resistance and went through three typical stages of cavitation erosion. The coating microstructure and heat-treatment procedure had a direct impact on the cavitation erosion resistance[11].
2. Xiaoben Qi et. al (2020)-Using phase analysis, morphological observation, microhardness testing, and coating lifetime evaluation, it was determined how heat treatment affected the microstructure, wear resistance, and thermal shock resistance of nano-WC particle strengthened Ni composite electrobrush plating coatings. After 550C heat treatment, the cauliflower
structure became more compact and element diffusion reinforced the coating-substrate interface, increasing the microhardness and coating lifespan. The microstructure of the substrate and coatings developed abnormally as the heating temperature rose, which led to the loss of the coating characteristics.
After heat treatment, the coatings' increased ability to withstand thermal shock resulted in improved microstructure, element diffusion, and the creation of new phases, all of which slowed the fracture start and propagation times
3. Nitesh Vashishthaet al. (2017) examined how heat treatment (300–
950 °C) affected the friction and abrasive wear behaviour of the coatings WC-12Co and Cr3C2- 25NiCr. At lower loads, the heat- treated coating's abrasive wear rate reduced with temperature increases up to 550 oC, however an upward trend was seen at higher loads. The coefficient of friction fell between 550 and 750 °C before trending upward.
Abrasive wear resistance was primarily impacted by phase transitions and variations in mechanical characteristics. On the basis of the respective contributions of mechanical wear and oxidative wear, the friction behaviour of heat treated coatings was explained. To detect the abrasive wear regime and changes in wear processes and failure modes, a severity of contact map was used[12].
4. S.A. Alidokh et. al (2016)-. A composite coating of Ni-10.5vol% WC was produced by spraying a mixture of Ni-36.2vol% WC using modified feedrates. Micro structural analysis, including the morphology of the coating's top surface and polished cross sections, was used to assess the influence of WC on Ni deposition.
The addition of WC to the Ni matrix increased the mechanical characteristics of coatings. Using a 6.35 mm diameter WC-Co ball, reciprocating sliding wear experiments were used to examine the wear behaviour of coatings. With a track length of 10 mm, a sliding speed of 3 mm/sec, and a standard
load of 5 N, all tests were carried out in dry air. More resistant to wear were WC-Ni coatings[13].
5. S. Matthews et al. (2021) used WC- 17wt%Co poeder for thermal spray coatings tha heat treatment was done. Up to 814 °C, the powder exhibited neither an exothermic nor an endothermic reaction; however, temperatures above this point generated a significant endothermic peak that persisted until 935 °C.
Analysis of materials that were heated below and beyond these DSC peak temperatures, however, was unable to pinpoint the exact mechanism causing this endothermic response. While the plasma Ar-He coating produced two exothermic peaks at 705 C and 800 C, the plasma Ar-H2 coating showed exothermic peaks at 700 C, 750 C, and 830 C. Despite accounting for each of the DSC peaks, the HVOF coating produced a broad peak from 665 C to 708 C [14].
6. TSAI-SHANG HUANG (2011) investigated the microstructure and characteristics of thermal sprayed by applying WC-CrC-Ni coating. Due to its excellent anti-wear and corrosion resistance qualities, hard chrome plating was chosen for this application. Different types of materials are employed with thermal spreads like WC/17Co or WC/10Co 4Cr, however hard chromium has substantially lower wear rates for both contacting and coating materials. The WC-Co is the most popular thermal spread tungsten carbide coating. It is made up of hard WC particles that are mixed with a robust metallic matrix through a procedure known as phase sintering.
The results indicated that the coating had poor corrosion resistance but good wear resistance. Ni is utilised, though, to boost its corrosion resistance.
7. Mishra T. K et al. (2022) WC-12Co cladding was examined. First, the cladding was deposited by using a domestic microwave of 900 W and 2.45 GHz frequency. Then, heat treatment was done by using an electrical muffle furnace at three different temperatures 400 °C,
600 °C, and 800 °C. The result showed that variation of temperature influences the phase change and mechanical property. Cladding at 400
°C and 600 °C sowed dense eutectic microstructure due to recrystallization of grain.
2.1 Need of Work
The use of conventional heating is not recommended since it results in materials with poor microstructure, cracks, residual stress, porosity, and distortion. However, microwave heating works at the molecule level and provides a homogeneous microstructure with little porosity and microcracks. An efficient and simple technology that helps to increase wear resistance is microwave cladding.
Machine wear is to blame for surface damage and a reduction in component life in both agriculture and automobiles.
Surface failure from wear occurs when agriculture machinery comes into direct contact with harsh abrasive particles.
This is a severe challenge and affects the cost of replacement as well as labor costs and downtime after studying several literary works. The literature on heat treatment of Ni-Wc coating is rare so it needs to investigate of the effect of heat treatment on Ni-Wc coatings.
2.2 Objective of Work
1. To Investigate the microstructure and phase formation after and before the heat treatment of Ni-Wc coatings.
2. To Investigate the effect of heat treatment on the hardness and porosity of Ni-WC coatings.
3. To Investigate the effect of heat treatment on abrasive wear properties of WC-Ni coatings.
4. To correlate these properties and represent in a graphical manner.
3 MATERIAL & METHOD
The goal of this chapter is to define the materials used for this work and methods adapted for experiments It includes a selection of coating material, deposition method and different experiments and testslike hardness, wear test, and microstructure.
3.1 Specimen Selection
For this current work, ASI 1020 steel was used as a substrate. The AISI 1020 steel possesses the following chemical composition.
Table 3.1 Specification of AISI 1020 Steel
Carbo
n,C Manganese
(Mn) Sulphu
r(S) Phosph
orus (P) Iron (Fe) 0.20% 0.30%-
0.60% 0.05% 0.04% 99.08
%- 99.53
% 3.1.2 Sample preparation
For the dry pin on the disc tester's wear specimen, a cylindrical bar made of AISI 1020 grade steel with a diameter of 12 mm was chosen. These cylindrical specimens were bought from Nextgen Engineering in Mumbai, and band saw equipment was used to prepare the specimens. The table below provides the specimen's precise size.
Table 3.2 Dimensions of the wear samples
Dimensions Diameter
(mm) Length (mm)
Size in mm 12 25
3.1.3 Microstructure specimen
In order to find a microstructure rectangular samplesle of 25x25x6 mm size were used for characterization including SEM and XRD.
3.2 Coating powder
The Hoganas made 1060 grade Ni powder was used for coating depositions. This powder was further modified with tungsten (W) powder at the percentages of 10% The ball Milling process was used to mix the above powder in clockwise and anti-clockwise directions to ensure uniform mixing. The chemical compositions of powders are mentioned below.
Table 3.2 Chemical composition of selected powders.
3.3 Powder selection and depositions For the coating deposition, powders with particle sizes of 45 20 m and 99.9%
purity, such as Ni and WC were chosen.
Powder C% Cr% Si% Fe% B% Ni%
Ni 0.75 14.8 4.3 3.7 3.1 Balance
WC 4.0 - -
MECPL, Jodhpur provide these powders (India). The 10 wt% WC powders were mechanically mixed with WC-12Co powder using a ball mill grinder operating at a speed of 200 RPM for one hour in the forward direction and back word direction..
At M/S MECPL, Jodhpur, changed and unmodified coatings were applied to utilise the HVOF coating deposition process using the HVOF gun (model HVOF HIPO JET2700, MEC, India) (India).
The coating was 300 µm thick. To remove precipitate impurities and moisture, the powder was warmed to 200 °C in an electric muffle furnace for one hour before coating. Coating parameters are provided in Table 3.4 Table 0.1 HVOF Coating Deposition Parameters
Table: 3. 3Coating parameters
Parameter Value
Oxygen pressure (kg/sq.cm) 10
Oxygen flow (slpm) 270
LPG pressure (kg/sq.cm) 7
LPG flow (slpm) 65
Air pressure (kg/sq.cm) 6
Air flow (slpm) 600
Powder feed rate (g/min) 45
Powder disc (rpm) 6
Nitrogen carrier gas flow (scfh) 20 Carrier gas pressure (kg/sq.cm) 6
Working distance (mm) 180
Figure 3.1 Coated wear samples 3.4 Morphology Investigation
The polished specimen was next chemically etched in accordance with ASTM B657 standard using nine parts K3Fe(CN)6+, one part NaOH, and one part distilled water.
For SEM and XRD investigation the polished coated samples of size 5mm
×5mm cut from 5cm×5cm coated samples using EDM wire cut machine with the addition of coolant to shield the coated
sample from heat dissipated during cutting.
3.5 SEM and X-ray diffraction
The scanning electron microscope test using JSM-6390LV, Jeol, Japan along with energy dispersive spectroscopy (EDS)of powder and coatings to find out microstructure and elemental analysis.
Figure 3.2 Coated rectangular specimen
X-ray diffraction (XRD) was used in conjunction with a Rigaku Smart Lab 9 KW XRD diffract meter and Cu-K radiation with a wavelength of 1.5406 to examine the phase development of feedstock powder and coated samples 9 Figure (3.3). On VNIT, Nagpur, the X-ray Diffraction (XRD) test was carried out.
The coated samples utilised for the XRD analysis were cut from coated samples measuring 5 cm by 5 cm using an EDM wire cut machine. The applied voltage and current were kept at 0.02°/s, 40 kV, and 20 mA for the XRD test's scanning speed.
In all samples, the range of the two theta diffraction angle variation was between 10° and 90°. The sample for XRD measurement, the XRD Rigaku Smart Lab, are shown in Figure- 3.4.
Figure 3.3 JEOL JSM-6390 LV SEM instrument
Figure: 3.4 XRD test showing (a) XRD Rigaku Smart Lab
3.6 Heat Treatment
An electrical muffle furnace maximum range of 1200° C was usedfor the heat treatment of cladded samples. Four different temperatures 400° C, 600° C, and 800° C were selected for heat treatment. The heating rate was 10° per minute. This sample was heated for 30 minutes and the soaking time was one hour and allowed furnace cooling in the controlled atmosphere inside the furnace.
3.7 Measuring microhardness and porosity
The coated specimens' microhardness was assessed in accordance with ASTM E 384- 2016 standard. 300 grams of stress was applied to a Vickers microhardness tester for a dwell time of 15 seconds to measure the material's hardness as shown in Figure 3.5. An average reading was taken for the outcome after five different readings were taken at five distinct locations in the cross-section. Through the use of Image-J software and SEM pictures, the porosity of the coated surfaces was assessed using the area percentage counting method.
Figure: 3.5 Vickers microhardness tester
3.8 Abrasive Wear
An abrasive wear test was performed on a pin-on-disc wear tester (TA-200LE, Magunun Engineers, Bangalore, India) as shown in Figure 3.6. Silicon carbide (100 μm size paper) was used as a counter surface against coated pin specimen of dimensions 12mm diameter and 25mm length. These tests were formed at 40 N loadat 100 rpmafter a sliding distance of 1000 meter sliding distance. The abrasive paper was put on a rounded disk of diameter165 mm and thickness of 6 mm.
Wear is measured in terms of height loss by A LVDT, mounted on a pin and disc wear tester. The coefficient of friction and frictional force was also continuously observed and noted separately during the individual sliding test. Acetone was used for cleaning the specimen before and after weigh loss measurement.
Figure 3.6 Schematic diagram of pin- on-disc friction and wear test rig 4. RESULT AND ANALYSIS
The aim of this chapter to describe the detail information of rest obtainted after investigation of different experiments.
4.1 SEM of feedstock powder
SEM images of the powder is shown in Figure 4.1. The image exhibits that Ni powder particles possess spherical shapes and are agglomerated with WC powder.
The spherical powder shape helps to smooth the flow during coating depositions.
Figure 4.1 SEM images of feedstock powders
4.2 SEM images of coatings
The scanning electron microscopy (SEM) images of Ni-WC (a) without heat treatment and (b, c, and d) heat treatment at 400° C, 600° C, and 800° C respectively are shown in figure 4.2. Ni- WC coating shows pores microstructure in a high-resolution image. Whereas the specimen with heat treatment at 400 ° C shows compertavelly dense but pores microstructure as shown in Fig. 4.2 (b).
When heat treatment temperature up to 600° C exhibits dense micristrure with fever pores as shown in Fig. 4.2 (c). After that, if the heat treatment temperature up to 800 ° C the extra deposition of carbide particles is seen in SEM images as shown in Fig. 4.2 (d). At higher temperatures distortion of the boundary of particles takes place and WC decomposed in solid and liquid which increases the separation of particles.
The EDS result of Ni-Wc coating is shown in Fig. 4.3 which confirms the presence of different elements including NI, WC and Cr Fe as an impurity.
Figure: 4.2 SEM images of Ni-WC (a) without heat treatment and (b, c, and
d) heat treatment at 400° C, 600° C, and 800° C respectively
Figure: 4.3 EDS of Ni-Wc coatings
4.3 XRD Analysis
XRD diffraction patterns of Ni-WCwithout heat treatment and heat treatment at 400° C, 600° C, and 800° C respectively are shown in Fig 4.4.
Figure 4.4 XRD pattern of Ni-Wc coatings at the different heat
treatment temperatures
There is a larg hump and deviations are seen between the theta angle of 30° to 50°
due to the formation of W2C phase. The decomposition of carbide particles is responsible for the W2C phase as temperature increases formation of W2C phase reduces. This confirms that heat treatment plays a significant role to reduce porosity and the makes microstructure dense.
4.4 Porosity analysis
The porosity of Ni-WC without heat treatment and heat treatment at 400° C, 600° C, and 800° C respectively are shown in Fig 4.5. Porosity decreases up to 600 ° C due to dense microstructure and good bonding between carbide particles.
After that separation of particles increases due to boundary distortion this results increment of porosity.
Figure 4.5 Porosity of coatings at the different heat treatment temperatures
4.5 Microhardness
The microhardness of Ni-WC without heat treatment and heat treatment at 400° C, 600° C, and 800° C respectively are shown in Fig 4.6. The microhardness increases with increasing heat treatment temperature. The specimen without heat treatment and heat treatment at 400° C, 600° C, and 800° C exhibits 620, 646, 745, and 710 HH0.3 hardness. The heat- treated sample at 400° C, 600° C, and 800° C exhibits 4.2, 20.2 and, 14.5 % higher hardness as compared to the sample without heat treatment. The result shows that coating with heat treatment at 600 ° C possesses higher hardness due to dense micmicrostructure.
Figure 4.6 hardness of coatings at the different heat treatment temperatures 4.6 Abrasive wear
The abrasive wear of Ni-WC without heat treatment and heat treatment at 400° C, 600° C, and 800° C respectively are shown in Fig 4.7. A weight loss method was adopted to find out the wear. The Ni- Wc coating without heat treatment exhibits higher weight loss due to its porous structure. When heat treatment temperature increases the weight loss shows decreasing trend up 600 ° C. After that wear starts increasing. The Ni-WC (without heat treatment), heat-treated coatings at 400° C, and 800° C exhibit 15.89, 8.23 and, 3.5.5 % higher wear as compared to the 600° C heat treatment coating. The minimum wear of coating at heat treated at 600° C is attributed the dense microstructure and higher hardness. These results show the heat treatment increases the hardness and reduces the porosity and wear of the Ni- WC coating up to an optimum heat treatment temperature of 600 ° C.
Figure 4.7 Wear of coatings at the different heat treatment temperatures 4.7 Coefficient of friction
The abrasive wear of Ni-WC without heat treatment and heat treatment at 400° C, 600° C, and 800° C respectively are shown in Fig 4.8. Coating at heat treatment at 600° C exhibits showed a higher coefficient of friction followed by a decreasing trend at 800° C, 400° C and coating without heat treatment shows the minimum coefficient of friction. The higher COF of 800° C heat-treated coating is due to less wear whereas coating without heat treatment exhibits a minimum coefficient of friction due to higher wear.
Figure 4.8 COF of coatings at the different heat treatment temperatures 5 CONCLUSION
Abrasive wear is a major factor in the breakdown of many industrial devices and the rising cost of operation and maintenance. Due to its diverse mechanical and physical qualities, low- carbon steel is frequently employed in industries. Because of its excellent mechanical qualities, including toughness, low-carbon AISI 1020 steel is widely utilized in industries for the production of various mechanical components. However, AISI 1020 steel has poor surface characteristics, including a reduced ability to resist
0 0.1 0.2 0.3 0.4 0.5 0.6
0 200 400 600 800 1000
COF
Time (sec)
400° C 800° C 600° C 0° C
abrasive wear. In order to improve the surface characteristics and boost wear resistance, surface modification is necessary.
On the basis of the present work following conclusions are made
1. Heat treatment significantly makes the microfeature dense and reduces the pores’ structure. Coating at 600
° C exhibits dense microstructure.
2. Eds result to confirm the presence of NI and WC as main elements.
3. XRD result shows that heat treatment reduces the deviations between the theta angle of 30 ° to 50
° due to the formation of W2C phase.
And heat treatment reduces the formation of W2C phase hence reducing the decomposition.
4. Porosity decreases up to 600 ° C due to dense microstructure and good bonding between carbide particles.
After that separation of particles increases due to boundary distortion this results increment of porosity.
5. The specimen withoutheat treatment and heat treatment at 400° C, 600°
C, and 800° C exhibits 620, 646, 745, and 710 HH0.3 hardness. The heat-treated sample at 400° C, 600°
C, and 800° C exhibits 4.2, 20.2 and, 14.5 % higher hardness as compared to the sample without heat treatment.
6. The Ni-WC (without heat treatment), heat-treated coatings at 400° C, and 800° C exhibit 15.89, 8.23 and, 3.5.5 % higher wear as compared to the 600° C heat treatment coating.
The minimum wear of coating at heat treated at 600° C is attributed the dense microstructure and higher hardness.
7. Coating at heat treatment at 600° C exhibits showed a higher coefficient of friction followed by a decreasing trend at 800° C, 400° C and coating without heat treatment shows the minimum coefficient of friction.
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