Analyzing the Cooling Rate and Its Effect on Distribution of Pattern and Size of the Titanium Diboride Particles Formed

Department of Mechanical Engineering, B. V. Raju Institute of Technology, Narsapur, Telangana, India Head of School, Science and Engineering, Curtin University Dubai, Dubai, UAE Department of Mechanical Engineering, Loyola-ICAM College of Engineering and Technology, Chennai, India Department of Mechanical Engineering, Marri Laxman Reddy Institute of Technology and Management, Hyderabad, India Department of Mechanical Engineering, WOLLO University, Kombolcha Institute of Technology, Kombolcha, Ethiopia Post Box No: 208


Introduction
e cast aluminium components are used in automotive industries due to its more strength-weight ratio, outstanding castability, and corrosion resistance [1,2]. e ex situ method is involved for the fabrication of particulate matter reinforced metal matrix composites (PRMMCs) by conventional ex situ method due to its isotropic properties, ease of fabrication, and the lower cost. e reinforcement is added directly to fabricate the ex situ composites [3,4]. In in situ method, a chemical reaction of reinforcements inside the composites takes place to synthesize the composites. To identify the behavior of in situ particles, a small work was carried out in the aluminium matrix composites [5]. e in situ metal matrix composites have a good attraction characteristic because of their good bonding strength and well distribution of fine reinforcement [6,7]. It was found that the study was concentrated on fabrication and the mechanical properties of the reinforcement such as SiC, Al 2 O 3 , TiC, and B 4 C. Various researchers have performed high-performance applications focusing on TiB2 as the reinforcement as of its high elastic modulus and high thermal conductivity [8,9]. Also, it does not react with the molten aluminium. e casting defects such as oxide films, porosity, and other inclusions will strongly disturb the mechanical behavior of the cast aluminium alloys [10,11]. However, because of the stiffness, hardness, and improved tensile strength, the aluminium-based MMCs are preferred compared to the base matrix alloy [12][13][14]. e fabrication of aluminium-based MMCs is done by addition of SiC, Al 2 O 3 , TiC, CBN, and TiB 2 . Out of these ceramic-based reinforced particles, TiB 2 is used mostly because they possess hardness, maximum tensile strength, and compressive strength [15,16].
Because of the very clean and size of particles in the interface of the in situ method, the fabrication of Al/TiB 2 MMCs is preferred. Also, the increased tensile strength and fatigue strength is due to the very fine particles [17].
In the in situ fabrication method, two salt powders such as K 2 TiF 6 and KBF 4 were used as reinforcement. ey were mixed in measured proportion and then poured to the aluminium melt slowly. e mixture was stirred manually to endorse the reaction between salts with the help of a manual graphite rod. e floron gas was inserted in the melt to avoid formation of gases which will create the casting defects such as blow holes [18,19]. Later, the melt was kept in hold to synthesize TiB 2 particles that grow in size with holding time [20,21].
e Al/TiB 2 melt was poured into the mould, so the falling elevation will be the possible turbulence that occurs during filling. e fragmented TiB 2 particles are created due to the turbulence, and also a variation in distribution occurred at different locations. It occurs because the cooling rate and turbulence were attributed and also due to the influence of melt fluidity [22,23]. e above parameters were analyzed, and their effects are understood clearly from the SEM micrographs captured from the cast ingot at six different locations.

Experimental Work
An in situ method was used to fabricate Al/TiB 2 MMCs through salt metal reaction. ree different melt temperatures were maintained, such as 750°C, 780°C, and 810°C. Also, three dissimilar holding times were maintained after mixing of entire salt such as ten minutes, twenty minutes, and thirty minutes before pouring into the permanent molds. rough the same procedure, totally nine ingots were fabricated with different combinations, pouring temperature, and holding time [24]. e size of the reinforced particle is not the same as in the melt because of the parameters' fluidness and disorder at different places of the ingot and the local cooling rate of the casting [25].

Results and Discussions
At location 23, the temperature-time curve indicates maximum cooling rate and turbulence during filling out of twenty-four different locations. Also, it was found that the fluidness reaches its maximum range at the maximum pouring temperature.
Also, here we discuss the effect of cooling rate at location 23. is location is marked in the bottom surface of the ingot, and the cooling rate and the fluidity are maximum at this location at 810°C pouring temperature. Additionally, the falling height of the melt during the filling process is considered to be maximum. Because of the abovementioned reasons, at location 23, the turbulence will be maximum. Because of these reasons, the circulation will be maximum at 810°C, and it will cause the TiB 2 particles to fragment. Hence, the TiB 2 particles get entrapped quickly because of maximum cooling rate, and the casting at this location is freezed [26].
Moreover, more TiB 2 particles are distributed at this location at 810°C and the TiB 2 particles formed various clusters in this zone as 70%-80%.
Here, we discuss the effect of cooling rate at location 21. is location is marked in the middle surface of the ingot; the cooling rate and the fluidity are modest at this location at 810°C pouring temperature. Additionally, the falling height of the melt during the filling process is considered to be average. Because of the abovementioned reasons, at location 21, the turbulence will be average. Because of these reasons, the circulation will be maximum at 810°C, and it will cause the TiB 2 particles to fragment. Hence, the TiB 2 particles get entrapped quickly because of maximum cooling rate, and the casting at this location is freezed [27,28].
Moreover, more TiB 2 particles are distributed at this location at 810°C and the TiB 2 particles formed various clusters in this zone as 60%-70%.
In this paragraph, we discuss the effect of cooling rate at location 19. is location is marked in the top surface of the ingot; the cooling rate and the fluidity are very low at this location at 810°C pouring temperature. Additionally, the falling height of the melt during the filling process is considered to be very less. Because of the abovementioned reasons, at location 19, the turbulence will be average. Because of these reasons, the circulation will be maximum at 810°C, and it will cause the TiB 2 particles to fragment. Hence, the TiB 2 particles get entrapped quickly because of very minimum cooling rate, and the casting at this location is freezed. Most of the TiB 2 particles were trapped at locations 23 and 21 already. Hence, very small particles settled down in this particular location.
Analyzing at location 1, the falling height and the cooling rate were minimum. Due to the effect, most of the particles 2 Advances in Materials Science and Engineering Advances in Materials Science and Engineering 3 were trapped at the bottom of the ingot at location 1, which was found to have fewer TiB2 particles through SEM micrographs. Also, it covers 40%-50% area in the SEM micrograph.
e friction between the aluminium matrix and TiB2 particles was analyzed. e tribological characteristics showed better performance than conventional material.  Also, the distribution of TiB 2 particles at different locations for less holding times and pouring temperatures was found to be low, which is tabulated in Tables 1 and 2.

Conclusions
e TiB 2 particles were found to be more at location 23 because of the very high cooling rate.
e TiB 2 particles were found more at locations 23 and 21 due to the very high turbulence. When the circulation of the fluid is more, the fluidity is also more.
Also, the tribological characteristics showed significant improvement on the basis of hardness. However, the reinforced particles get trapped quickly when the cooling rate was very high at these locations.

Data Availability
No data were used to support this study.