Elsevier

Composites Communications

Volume 22, December 2020, 100458
Composites Communications

Short Communication
Influence of Al2O3 and ZrO2 alloying on microstructure, hardness and flexural strength of Ni based functionally graded composites by vacuum sintering

https://doi.org/10.1016/j.coco.2020.100458Get rights and content

Highlights

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    Ni based Al2O3 and ZrO2 alloyed FGCs were consolidated by vacuum sintering.

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    Graded composition of Ni/Al2O3–ZrO2 composites were analyzed by SEM-EDS spectra.

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    Hardness of Ni FGC improved to 20% by alloying of Al2O3 and 30% by alloying of ZrO2..

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    Combined alloying of Al2O3 and ZrO2 in Ni Matrix significantly improves the hardness and flexural strength of FGCs.

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    Fine grained structure and Al–Zr–O oxide dispersions are observed to enhance the mechanical properties of the Ni/Al2O3–ZrO2 FGCs.

Abstract

This work investigates the effect of Al2O3 and ZrO2 addition on microstructure and mechanical properties of Ni based functionally graded composites (FGCs). The cylindrical pellets of different compositions of three layered FGCs were prepared through mechanical alloying followed by compaction and conventional sintering. The sintering was conducted at 1200 °C for 90 min under vacuum atmosphere. Microstructure, hardness and flexural strength of the samples were examined and comparisons were made between Al2O3 and ZrO2 alloying. The FGCs with alloying of Al2O3 along with ZrO2 shows the highest hardness of 258.1 HV0.05. The flexural strength of FGCs improved to 18% by combined alloying of Al2O3 and ZrO2. The homogeneous dispersion of refined powder particles and precipitation of Al–Zr–O oxides appears to be responsible for the improved properties of Ni based FGCs.

Introduction

Functionally graded composites (FGC) are new generation of engineering materials wherein the material composition varies gradually in some directions to achieve unique material properties [1]. FGCs are ideal applicants for the applications requiring multi-functional performance [2]. The metal/ceramic composites can be designed to reduce thermal stresses and take advantage of the mechanical behavior of metal and corrosion resistance of the ceramic [3].

Due to the high corrosion resistance and mechanical properties of the constituent materials, the metal/ceramic FGCs can exhibit good service performance under severe environments [4]. Bulk functionally graded materials have been modified for better performance by several methods, such as electrophoretic deposition [5], centrifugal-slip casting [6] and powder metallurgy [7].

Bykov et al. [8] fabricated the seven layered Ni/Al2O3 composite via microwave sintering. According to their research, the Al2O3 rich composite layers showed less porosity compared to Ni rich layers. EL-Wazery et al. [9] investigated the microstructure and mechanical properties of Ni/ZrO2 FGMs processed through powder metallurgy. The results of this research showed that the tensile strength and bending strength decreases with increase in nickel content due to weak bonded ceramic/metal interface. Miazga et al. [10] investigated the effect of alumina particle size on properties of Ni– Al2O3 cermet composites by gel-casting and reduced atmosphere sintering. The results revealed that the sintered density increased to 97% by dispersion of fine particles of Al2O3.

Bhattacharyya et al. [11] investigated the hardness and flexural strength of five layered Ni/SiC functionally graded material (FGM) by powder metallurgy route. They demonstrated that the increase in flexural strength attributed by reduction of residual stress in FGM due to manufacturing process with increased number of layers. Jojith et al. [12] studied the hardness and wear rate of Ni based TiC dispersed functionally graded composites under heat treated condition. They investigated that the Ni based FGMs solution analyzed at 550 °C gave better hardness and wear properties.

From the above literature, there is limited knowledge base on nickel based functionally graded composites processed by powder metallurgy. And also, none of the reports available on the effect of combined alloying of alumina and zirconia during the development of Ni FGCs. In the present study, a three layered Ni/Al2O3–ZrO2 FGC fabricated by powder metallurgy were reported for the first time. The influence of Al2O3–ZrO2 alloying on microstructure, hardness and flexural strength of FGCs is also presented.

Section snippets

Experimental procedure

Elemental powders of alumina (Al2O3) and zirconia (ZrO2) with purity > 99.8 wt% and particles size 10 μm, and nickel (Ni) with purity > 99.7 wt% and particles size 40 μm were used as the raw materials. The functionally graded composites (FGCs) are designed with three layers of variation in the Ni and Al2O3–ZrO2 compositions. Nine different possible combinations of Ni based FGC with Al2O3 and ZrO2 were prepared. Table 1 presents the detailed compositional distribution of three layered FGCs. The

Micro-structural studies

Fig. 1a shows a backscatter electron (BSE) image of Ni/Al2O3–ZrO2 three layered structure. The bonding between nickel and ceramic particles in layered structure is well and every layer had suitable linkages with no crack at the interface were seen.

The Ni/Al2O3 composite (Sample A) layered area and the corresponding EDS spectra is shown in Fig. 1b. As seen, coarse sized alumina grains have irregular in shape and distributed in Ni matrix. Fig. 1c shows the microstructure of Al2O3–ZrO2 alloyed Ni

Conclusion

This study investigates the effect of alloying elements such as Al2O3 and ZrO2 during the development of Ni based three layered functionally graded composite. Nine samples of different combinations with alumina and zirconia was prepared. The microstructural variation with reference to layered composition is noticed. The alloying elements of FGCs are confirmed with SEM-EDS analysis.

The following results were emerged from the present study.

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    FGCs produced by Al2O3 and ZrO2 alloying through powder

CRediT authorship contribution statement

K. Ananta Bhaskararao: Conceptualization, Investigation, Methodology, Writing - original draft. G. Ranga Janardhana: Writing - review & editing, Supervision, Validation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The experiments and SEM analysis were carried out in International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), India. The mechanical testing was carried out at the Anna University College of Engineering, Chennai, India.

References (18)

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