Advantages, Case Study, Challenges, and Future Scope


The advantages of the UAS are summarized in the following points:

  • • Ultrasonic vibration accelerates the sintering diffusion process during the initial stage of sintering.
  • • Better properties such as relative density, electrical conductivity, and hardness can be achieved at low sintering temperature as compared to the conventional sintering process.
  • • Ultrasonic vibration enhanced the number of dislocations during sintering and resulted in the fine microstructure.
  • • Ultrasonic vibration enhanced the chemical reactions during sintering at a faster rate.
  • • Ultrasonic vibration homogenously mixed the metal powder particles to lower the porosity in the sintered specimen.
  • • Ultrasonic vibrations removed the oxide layer on the powder particles by rubbing at room temperature and exposed pure metal surfaces for sintering.

Case Study

To check the efficacy of the ultrasonic vibration effect on the sintering, few experiments have been carried out as a case study. The pressureless loose sintering of copper spherical powder is carried out with 20 pm ultrasonic vibrations. The metal powder particles were procured from MEPCO, India, with a particle size of 5-50 pm. The details of the experimental setup and measurement techniques used for the case study were provided in the previous studies [17,22]. The concern of the case study is to study the effect of ultrasonic times on the density and microstructure of the sintered particles. The comparison of UAPS with CPS was also studied. The sintering was carried out at 800°C with 4°C/min heating and cooling rate with 45 minutes of the soaking time. Two different ultrasonic vibration experiments were carried out with the same sintering cycle. First, to check the ultrasonic vibration time, ultrasonic vibrations were provided for heating rate from 600°C and for different times (3, 6, 9, 12, 15, 18, and 21 minutes) of soaking time. The vibrations were kept off for the CPS and compared with UAPS in terms of relative density and SEM morphology.

Figure 1.13 represents the effect of the ultrasonic time on the relative density of the sintered part and the relative density difference with CPS. It was observed that after 15 minutes of soaking time, there was no significant effect of ultrasonic vibrations on the sintering. The 10% increase in relative density as compared to CPS was observed. During the initial stage of sintering, surface mechanism plays a significant role [50]. The ultrasonic vibrations increased the local temperature between the particles and reduced the material flow stress for better densification. Due to this, small particle merged into the large particles faster as compared to the conventional method and provided higher neck growth. Using the SEM, morphological images of the sintered particles are also shown in Figure 13. It was observed that the

Effect of ultrasonic vibration time on the relative density of sintered copper with SEM images

FIGURE 1.13 Effect of ultrasonic vibration time on the relative density of sintered copper with SEM images.

Effect of ultrasonic vibration entry time on the relative density of the sintered copper

FIGURE 1.14 Effect of ultrasonic vibration entry time on the relative density of the sintered copper.

ultrasonically treated samples have larger necks between the particles as compared to the conventionally sintered particles. The grain-boundary diffusion mechanism was observed earlier in the case of UAPS as compared to CPS. Therefore, ultrasonic treatment during the initial stage of sintering accelerates the sintering mechanism and provides better densification at low temperature and less soaking time.

The next phase of experiments was conducted to check the efficacy of ultrasonic vibration’s entry time. First, the vibrations were given from the starting of the soaking time (i.e., 0 minutes). Then, vibrations were given after 9 minutes of soaking time and later after 18 minutes of soaking time. These experiments were also compared based on the relative density and SEM morphological analysis. It has been observed that ultrasonic vibrations showed a significant effect from the starting of the soaking time. As the vibrations were given after 9 minutes of soaking time, 12% less relative density was observed as compared to the 0-minute entry results. Furthermore, after 18 minutes of soaking time, the ultrasonic vibrations showed an insignificant effect and the samples possessed 75% relative density similar to CPS samples. The SEM morphological results (ref. Figure 1.14) confirmed that the ultrasonic vibrations enhanced the neck growth in the zero-entry time-treated samples as compared to other samples.

Challenges and Future Scope

In the manufacturing processes, there are several types of challenges regarding design, parametric variations, characterizations, and repeatability. In UAS, the major challenge is to provide directly ultrasonic vibrations to the specimen due to the high-temperature treatment. Different means of sources have been discussed in the literature. For nanoparticles’ sintering, direct transducer vibrations were used by the help of fixtures [25]. However, special attention was paid in the literature to the ultrasonic horn design and sintering accessories for the high-amplitude vibrations. The long-length horn design is still a challenge in UAS to prevent the damage of transducer and ultrasonic generator accessories from the furnace heat. The ultrasonic vibrations enhanced the initial stage of sintering in terms of large neck growth. The sintering conditions vary depending upon the type of materials, particle size and shape, and nature of sintering (pressureless, pressure-assisted, loose powder, etc.). Therefore, for such conditions, the effect of ultrasonic vibration times and vibration entry times will be different.


This chapter represents the fundamental mechanism and important parameters of the UAS. Ultrasonic vibrations reduced the material flow stress and increased the local temperature between the particles for homogenous diffusion. The horn design for the UAS process has been discussed in detail. Further, the working principle of the UAS was explained. The ultrasonic vibrations at room temperature removed the oxide layer by interparticle rubbing and exposed the pure metal surface to contact. The pure surfaces softened at high temperature using ultrasonic vibrations, thus leading to better surface diffusion. The important processing parameters such as ultrasonic power, ultrasonic vibration time, sintering temperature, particles’ shape and size, and pressure during sintering have been discussed. The case study regarding the sintering of copper particle was also given. It was revealed that the ultrasonic vibration entry has a significant effect on the diffusion of the particles. The advantages, major challenges, and future scope have been provided in the last segment of this chapter.


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