In the realm of advanced materials, the quest for novel compositions and fabrication methods has driven researchers to explore uncharted territories, seeking materials that exhibit remarkable mechanical properties and diverse functionalities. The mixing of metals and ceramics has been a focal point of this pursuit, yielding composites that combine the best of both worlds: the toughness of metals and the hardness of ceramics. Among these innovative combinations, ZrO₂-Cr-Ni based metal-ceramic blends with yttrium (Y) and cerium (Ce), synthesized through the versatile technique of powder metallurgy, have emerged as a captivating subject of study. The union of ZrO₂, Cr, and Ni brings forth a triad of elements that encompass intriguing mechanical attributes. Zirconia (ZrO₂), a well-recognized ceramic, exhibits a rare phenomenon known as transformation toughening, wherein it undergoes a phase transition under mechanical stress, effectively retarding crack propagation. Chromium (Cr), on the other hand, introduces corrosion resistance and oxidation stability, characteristics particularly attractive for applications in demanding environments. Nickel (Ni), with its exceptional ductility and thermal conductivity, complements this amalgamation by enhancing the overall toughness and thermal performance. The addition of chromium (Cr) and nickel (Ni) to ZrO₂ has been shown to improve mechanical properties, but recent research has pushed the boundaries further by incorporating yttrium and cerium as reinforcing agents, giving rise to ZrO₂-Cr-Ni based metal-ceramic blends. Zhang et al. (2019) ventured into the nuances of phase transformations, elucidating the impact of yttrium on the martensitic transformation of ZrO₂, a phenomenon central to its transformation toughening mechanism [1]. This intricate dance of phases was further deciphered by Li et al. (2020), who unveiled the role of cerium in influencing the kinetics of phase transitions and crystallite growth [2]. For instance, Sun et al. (2019) investigated the effects of yttrium oxide (Y₂O₃) on the mechanical properties of alumina-zirconia composites [3]. The addition of Y₂O₃ was found to enhance the strength and toughness of the composites, attributed to the formation of a fine-grained microstructure and phase transformation toughening. Similarly, Wu et al. (2020) examined the role of cerium oxide (CeO₂) as a sintering aid in zirconia ceramics. The inclusion of CeO₂ promoted densification and grain growth, resulting in improved mechanical properties [4]. Zhu et al. (2018) [2] investigated the fracture toughness of ZrO₂-Cr-Ni-Y-Ce composites and observed significant enhancement compared to the pure ZrO₂ matrix [5]. The researchers attributed these enhancements to the formation of yttrium-stabilized tetragonal zirconia phases, which transformed into monoclinic zirconia under stress, effectively impeding crack propagation. In a comprehensive study by Chen et al. (2020), cerium additions were found to increase the fracture toughness of alumina ceramics, a phenomenon attributed to the formation of cerium oxide precipitates at grain boundaries [6]. This intriguing phenomenon, coupled with the notable ability of cerium to scavenge oxygen vacancies, holds great promise in the context of metal-ceramic composites. The symphony of mechanical attributes resonates through the resonance of these blends, encompassing parameters such as fracture toughness, fatigue resistance, and wear behaviour. The stage on which these compositions perform spans the spectrum of biomedical applications, where materials are thrust into the crucible of human well-being. Dental implants, bearing the weight of mastication, find their resonance in the enhanced mechanical stability of these metal-ceramic blends. Orthopaedic implants, bridging the chasm of bone fractures, draw strength from the augmented load-bearing capacity of these composites. The biomedical orchestra extends further to include prosthetic components, surgical instruments, and drug delivery systems, all harmonizing to the tune of enhanced mechanical functionality. The mechanical behaviour of ZrO₂-Cr-Ni based metal-ceramic blends with yttrium (Y) and cerium (Ce) prepared through powder metallurgy has emerged as a topic of significant interest in materials science and engineering. This literature review aims to explore the current state of research and advancements in this area, shedding light on the synthesis, mechanical properties, microstructural characteristics, and potential applications of these composites. Chen et al. (2020) investigated the impact of cerium additions on the fracture toughness of alumina ceramics. The researchers observed an increase in fracture toughness due to the formation of cerium oxide precipitates at grain boundaries, effectively hindering crack propagation [7]. Lee et al. (2019) employed powder metallurgy to fabricate ZrO₂-Cr-Ni based metal-ceramic blends with yttrium and cerium. The study demonstrated the feasibility of the PM route in obtaining uniform distribution of Y and Ce within the matrix, leading to improved mechanical properties [8]. A key advantage of PM is the ability to tailor the composition and microstructure of the composites by controlling powder characteristics, mixing parameters, and sintering conditions. Several studies have explored the influence of powder characteristics, such as particle size and morphology, on the mechanical properties of the resulting composites (Chang et al., 2019) [9]. Saito et al. (2016) demonstrated that the addition of Y promoted the formation of a tetragonal zirconia phase in alumina-zirconia composites, imparting transformation toughening capabilities and mitigating crack propagation [10]. Wang et al. (2017) [11] demonstrated the successful fabrication of Y₂O₃ and CeO₂ doped ZrO₂-Cr-Ni powders through co-precipitation and subsequent reduction processes. The addition of Y and Ce was found to enhance the sinter ability of the powders, resulting in denser and more homogenous compacts. Moreover, the unique mechanical behaviour of zirconia, such as transformation toughening, was further enhanced by yttrium additions. Cui et al. (2019) [12] elucidated the toughening mechanisms in ZrO₂-Cr-Ni based composites with yttrium, showing that the transformation from the tetragonal to the monoclinic phase under stress effectively hindered crack propagation, leading to improved fracture toughness. Tensile tests have been conducted to assess the mechanical strength and ductility of the composites (Li et al., 2019). The addition of yttrium and cerium has been shown to improve the tensile strength and elongation of the composites [13]. Hardness measurements are another essential aspect of the mechanical characterization, as hardness directly influences the wear resistance and load-bearing capacity of the materials. The incorporation of yttrium and cerium has been reported to enhance the hardness of the composites due to the formation of solid solutions and grain boundary strengthening (Miao et al., 2022) [14].

The aim of present investigation is to systematically examine the correlation between sintering temperature and the resulting physical and mechanical properties of a ZrO2-Cr-Ni-Ce-Y composite material. By subjecting fabricated samples to a range of sintering temperatures, the research aims to elucidate the optimal temperature for achieving desired mechanical characteristics. Understanding how sintering temperature affects the properties of ZrO2-Cr-Ni-Ce-Y composites can lead to the production of materials with superior mechanical characteristics. This research provides valuable insights into the microstructural evolution of ZrO2-based composites during sintering. ZrO2-based composites are widely used in various high-tech applications, including aerospace, automotive, and biomedical fields. Enhancing their properties through precise control of sintering parameters can expand their applicability and performance in these demanding environments.

Zirconium oxide (ZrO₂), chromium (Cr), and nickel (Ni) were chosen as the base metallic constituents due to their better tensile mechanical properties and compatibility with the ceramic phase. Yttrium powder (Y) and cerium powder (Ce) were selected as dopants for the ceramic phase based on their ability to improve mechanical performance and phase stability [15]. High-purity zirconium dioxide (ZrO₂), chromium (Cr), nickel (Ni), and yttrium (Y) powders from suppliers as shown in Table 1 were used for this procedure. The reason behind the selection of these materials was based on the theory of atomic radius of these elements. These all elements have almost very similar or less differences in their atomic radius, which would be an approval factor in the selection of appropriate matrix for this metal-composite. Also, the dopants used for this composite have compatible atomic sizes to be fitted perfectly in the lattice spaces of the metal-composites [16].

To prepare the composite specific volume percentages of each component are as follows: 20% ZrO₂, 35% Cr, 35% Ni, 5% Cerium, and 5% Yttrium. Afterward the powders were mixed and homogenized using a high-energy ball milling in the depressurized steel chamber to ensure a uniform distribution of the dopants i.e., Cerium and Yttrium within the ZrO₂-Cr-Ni matrix. Before compaction process the composite was mixed with the binding agent. Iso-Propyl alcohol of concentration 90-95% was used for obtaining a well compacted and matrixed product. The homogenized powder blend was compacted into green bodies using a cold isostatic press (CIP), with the compaction pressure and dwell time optimized to achieve the desired density and eliminate any defects in the green bodies. The composite samples raw powders were mixed separately using a high-energy ball mill to achieve a sustainable powder blend. The mixed samples powder was transferred to a die set for compaction. A punch of Ø6 mm was used in compaction. Under controlled pressure and through CIP the powder mixtures were compacted. The pressure applied during CIP from 130 MPa to 660 MPa to achieve the desired density and compaction of the powders. The pressing time depends on the equipment, the density requirements, and the properties of the powders. The pressing time for CIP was taken around 11 to 13 minutes. It was performed at room temperature to avoid sintering or densification due to heat. Therefore, the temperature was kept at or close to room temperature during the pressing process. A controlled and gradual pressurization is often employed to prevent sudden pressure fluctuations and ensure uniform compaction. A depressurization rate of 174 MPa per minute was employed in CIP.

After that green bodies were sintered in a controlled atmosphere at specific temperature and duration. The sintering process is critical for promoting densification, grain growth control, and the formation of the desired microstructure in the composites. During sintering the temperature is critical parameter that determines the level of densification, grain growth control, the formation of the desired microstructure in the composites and the final mechanical properties of the sample. The compacted metal-composites were sintered at 1350°C for 3 hours 23 minutes. However, a keen record has been maintained by observing the sample at different temperatures i.e., at 850°C, 950°C, 1050°C, 1150°C, 1250°C and 1350°C. A controlled and gradual heating rate of 5.5°C per minute was employed to minimize thermal stresses and prevent cracking. The holding time i.e., 3 hours and 23 minutes was employed during sintering which allows sufficient densification and bonding between the powder particles. After the sintering, a controlled cooling rate like the heating rate was employed to avoid rapid thermal gradients and reduce the risk of cracking. During sintering of metal-based composites, a reducing atmosphere constituting hydrogen gas was prepared in the furnace to prevent oxidation and achieving better results. Figure 1 shows a graphical illustration of the composite fabrication procedure.

The study provides a comprehensive analysis of the microstructural evolution, density, hardness, and flexural strength of a sintered composite consisting of ZrO2-Cr-Ni-Ce-Y across various sintering temperatures. The key findings can be summarized as follows: