Investigation on Iron-Based Composite Through Microwave Hybrid Heating

Abstract

The austenitic stainless steel (SS316) is the most commonly used material among all the available stainless steel grades, due to its ease of availability and significant highly attractive features or properties. It contributes more than 70% of total steel production in the world. The attractive features include good corrosion resistance, formability, biocompatibility, and weldability along with high thermal stability, toughness, and ductility. However, components of SS316 have a limited lifespan due to poor frictional properties, non-hardenable, and low anti-wear properties under severe tribological conditions. The wear is the primary cause of the terrible failure of many engineering field machinery and their components like; automobile components contacting pairs, such as rolling element bearings, gears, traction drives, followers and cams, engine parts, etc. The sliding wear causes a substantial economic loss to the automotive industry due to the frequent replacement of tribological and sliding parts. Only the tribological contacts consume the world’s 23% of energy, of which 20% is employed to overcome friction, and 3% is used to remanufacture worn-out parts. A boundless requirement for wear-resistant materials exists to increase the working span of the parts and cut their annual repair and maintenance costs. The existing problem in SS316 stainless steel can be overcome by, adding varying proportions of reinforcements like of EWAC (Ni-based), hard carbides of WC, chromium carbide, MoC, vanadium carbide, and TiC for making composite castings. The traditional heating/melting methods or processes are in use for manufacturing composite materials. However, these methods have their limitations for controlling various metallurgical, and solidification defects, higher running costs, more energy consumption, long processing time, etc. To overcome these difficulties faced in the conventional and non-conventional casting process, microwave hybrid heating is a competent process to address these challenges. This process shows their capabilities for enhanced metallurgical, mechanical, and functional properties in processed or manufactured components. Very limited studies have been carried out on the processing of metallic materials, owing to the reflection of microwaves at room temperature, and hence, heating of such materials is very difficult. The capabilities of the process have been explored in the domain of sintering, joining, cladding, FGM, drilling, and casting. Hence, for the present work, microwave energy is utilized for the casting of Iron-based metal matrix composites from powder materials by using a multimode microwave applicator operated at 2.45 GHz and a maximum allowable power of 900 W. Hence, for the present work, microwave energy is utilized for the casting of Iron-based metal matrix composites from powder materials by using a multimode microwave applicator operated at 2.45 GHz and a maximum allowable power of 900 W. The principle of microwave hybrid heating (MHH) was used by using charcoal powder as a susceptor; for melting and casting of the raw materials. The sound cast of various selected compositions is developed within 28-35 minutes of microwave radiation exposure. For the current investigations commercial SS316 powder was selected as matrix material and EWAC(Ni-based), WC-12Co, and Cr7C3 were used as reinforcements for the development of various metal matrix composite (MMC) castings. The matrix and reinforcement powders were premixed in a blending machine to get homogeneously mixed powders. The SS316+15EWAC, SS316+15EWAC+xWC-12Co (x=5, 10, and 15%), and SS316+15EWAC+xCr7C3(x=5, 10, and 15%) by wt.% of powders were prepared and pre-heated at 230° C and placed in graphite mold; which is exposed to microwaves for optimum duration of microwave radiations. The cavity was subjected to ambient cooling conditions to facilitate the solidification of the castings. The developed casts were characterized for microstructural analysis (using an optical microscope and FE-SEM equipped with EDS), X-ray diffraction (phase analysis), Grain size (using image J software), porosity (using microcam 4.1 as per B-276 standard) density (using Archimedes principle), mechanical properties (microhardness, and flexural strength) and functional characterization (dry sliding wear behavior). The volumetric heating nature of microwaves caused the formation of equiaxed grains throughout. The low porosity of the order of 0.85% and high density of 98% were achieved in the developed SS316 casts. The overall porosity and density vary from 0.85-3.8% and 95.14%-98% for different microwave-processed cast samples. The fine-grained cast of grain size 15.4±3 µm was achieved in SS316+15EWAC+15WC-12Co and overall it varies up to 30±5 µm. The grain growth in the composite cast is suppressed. In the XRD analysis of the SS316+15EWAC+xWC-12Co (x=5, 10, and 15%); phases of SiC, Cr23C6, Fe7W6, Co6W6C, W, and Ni4W were observed. Similarly, in case of SS316+15EWAC+xCr7C3(x=5, 10, and 15%), Fe, Fe3Ni2, Cr23C6, MoNi4, Mo2C, and Fe5C2 were observed. The Vicker’s microhardness of SS316 and SS316+15EWAC reveals microhardness of 237.69 ± 9 HV and 254.72 ± 16.92 HV. However, carbide-reinforced composite castings have SS316+15EWAC+15WC-12Co an average value of 681.23±253.94 HV, whereas, SS316+15EWAC+15Cr7C3 casts show 585.93 ± 203.33 HV. The flexural strength of SS316 cast possesses a 246.72 MPa, SS316+15EWAC possesses 272.81 MPa, SS316+15EAWAC+10WC-12Co possesses 381.23 MPa, and SS316+15EWAC+15Cr7C3 of 469.86 MPa. The dry sliding wear tests of the composite cast show lower cumulative weight loss in comparison to pure SS316 microwave casts during sliding due to higher Vicker’s microhardness and uniform dispersion of reinforcements in the matrix. The maximum cumulative weight loss of 67.2 ± 0.5 mg was for SS316 and the minimum weight loss was 12.2 ± 0.2 mg. The maximum cumulative weight loss of 12.2 ± 0.6 mg was obtained for SS316+15EWAC+xWC-12Co (x=5, 10, and 15%), and the minimum cumulative weight loss of 2.1 ± 0.2 mg. The de-bonding of carbides, smearing of tribo-film, delamination, shear, plastic deformation, pitting, craters, and cracks were observed in worn samples of the cast specimens. Taguchi's design of the experiment L27 orthogonal array was used for weight loss analysis. ANOVA analysis was carried out to find the optimized parameters and their impact on weight loss.