In this paper, we have studied the evolution of morphology and brazing behavior of Ag-28Cu alloy filler processed by high energy ball milling. The milling of the powder mixture was carried out for 40 h. The structural and morphological analyses were performed by the X-ray diffraction and scanning electron microscopy. The melting temperature of the braze filler was determined by differential thermal analysis. The filler wetting properties were assessed from the spread area ratio measurements on various Ti substrates. The results indicate that the ball milling can effectively depress the filler melting point and enhance the brazeability. The milled powder mixture showed Ag(Cu) solid solution with a crystallite size of 174-68 nm after 40 h. It was shown that the high energy ball milling can be a potential method to develop low temperature brazing fillers for advanced microjoining applications.

In this study, we have developed Sn-Ag alloy by a simple high energy ball milling technique. We have ball-milled the eutectic mixture of Sn and Ag powders for a period of 45 h. The milled powder for 45 h was characterized for particle size and morphology. Microstructural investigations were carried out by scanning electron microscopy and X-ray diffraction studies. The melting behavior of 45 h milled powder was studied by differential scanning calorimetry. The resultant crystallite size of the Sn(Ag) solid solution was found to be 85 nm. The melting point of the powder was 213.6oC after 45 h of milling showing depression of ≈6oC in melting point as compared to the existing Sn-3.5Ag alloys. It was also reported that the wettability of the Sn-3.5Ag powder was significantly improved with an increase in milling time up to 45 h due to the nanocrystalline structure of the milled powder.

Nanostructured thermoelectric materials receiving great attention for its high thermoelectric performance. In this research, nanostructured n-type Bi2Te2.7Se0.3 alloys have prepared using high energy ball milling and followed by spark plasma sintering. Also, we have varied ball milling time to investigate milling time parameter on the thermoelectric properties of n-type Bi2Te2.7Se0.3 powder. The powders were discrete at 10 min milling and later particles tend to agglomerate at higher milling time due to cold welding. The bulk fracture surface display multi-scale grains where small grains intersperse in between large grains. The maximum Seebeck coefficient value was obtained at 20-min milling time due to their lower carrier density. The κ values were decreased with increasing milling time due to the decreasing trend observed in their κL values. The highest ZT of 0.7 at 350 K was observed for 30-min milling time which was ascribed to its lower thermal conductivity. The Vickers hardness values also greatly improved due to their fine microstructure.

The current study were performed in order to assess the fabrication possibility of the metal-ceramic composites based on nanocrystalline substrates. The influence of the variable time of the high energy ball-milling (10, 30 and 50 h) on the structure, pores morphology and microhardness of Ti/ZrO2 and Ti/Al2O3 compositions was studied. The X-ray diffraction analysis confirmed the composite formation for all milling times and sintering in the case of Ti/ZrO2 system. Decomposition of substrates during milling process of Ti/Al2O3 system was also observed. Additionally, the changes of lattice parameter as a function of milling time were studied. The morphology of powders and the microstructure of the sintered samples were observed by scanning electron microscopy (SEM). Also, analysis of microhardness and pores structure were performed.

The Mn-Zn ferrite powders prepared by high energy ball milling were heat-treated, subsequently compacted and sintered by spark plasma sintering (SPS). Based on the observation of microstructure, the characteristics of samples after SPS were investigated and compared with ones after conventional sintering. The size of initial powders was approximately 650 nm and decreased to 230 nm after milling at 300 rpm for 3 h. After heat treatment at 973K for 1h, the milled powders became larger to approximately 550 nm in size again and the peaks of Mn2O3 disappeared in XRD patterns. In the samples after SPS, the Fe2O3 and MnZnFe2O4 phases decomposed at the higher temperatures than 1173K and 1373K, respectively, while only MnZnFe2O4 phase was detected in the samples conventionally sintered at 1273~1673K. As the sintering temperature increased, the relative density after SPS increased more quickly than that after conventional sintering. In particular, it reached approximately 99% after SPS at 1473K.

Mixture of nickel and titanium powders were milled in planetary mill under argon atmosphere for 100 hours at room temperature. Every 10 hours the structure, morphology and chemical composition was studied by X-ray diffraction method (XRD), scanning electron microscope (SEM) as well as electron transmission microscope (TEM). Analysis revealed that elongation of milling time caused alloying of the elements. After 100 hours of milling the powders was in nanocrystalline and an amorphous state. Also extending of milling time affected the crystal size and microstrains of the alloying elements as well as the newly formed alloy. Crystallization of amorphous alloys proceeds above 600°C. In consequence, the alloy (at room temperature) consisted of mixture of the B2 parent phase and a small amount of the B19' martensite. Dependently on the milling time and followed crystallization the NiTi alloy can be received in a form of the powder with average crystallite size from 1,5 up to 4 nm.

Mixture of nickel and titanium powders were milled in planetary mill under argon atmosphere for 100 hours at room temperature. Every 10 hours the structure, morphology and chemical composition was studied by X-ray diffraction method (XRD), scanning electron microscope (SEM) as well as electron transmission microscope (TEM). Analysis revealed that elongation of milling time caused alloying of the elements. After 100 hours of milling the powders was in nanocrystalline and an amorphous state. Also extending of milling time affected the crystal size and microstrains of the alloying elements as well as the newly formed alloy. Crystallization of amorphous alloys proceeds above 600°C. In consequence, the alloy (at room temperature) consisted of mixture of the B2 parent phase and a small amount of the B19’ martensite. Dependently on the milling time and followed crystallization the NiTi alloy can be received in a form of the powder with average crystallite size from 1,5 up to 4 nm.

The dispersion of nanoparticles in the host matrix is a novel approach to enhance the thermoelectric performance. In this work, we incorporate the TiC (x = 0, 1 and 2 wt.%) nanoparticles into a p-type Bi0.5Sb1.5Te3 matrix, and their effects on microstructure and thermoelectric properties were systematically investigated. The existence of TiC contents in a base matrix was confirmed by energy dispersive X-ray spectroscopy analysis. The grain size decreases with increasing the addition of TiC content due to grain boundary hardening where the dispersed nanoparticles acted as pinning points in the entire matrix. The electrical conductivity significantly decreased and the Seebeck coefficient was slightly enhanced, which attributes to the decrease in carrier concentration by the addition of TiC content. Meanwhile, the lowest thermal conductivity of 0.97 W/mK for the 2 wt.% TiC nanocomposite sample, which is ~16% lower than 0 wt.% TiC sample. The maximum figure of merit of 0.90 was obtained at 350 K for the 0 wt.% TiC sample due to high electrical conductivity. Moreover, the Vickers hardness was improved with increase the addition of TiC contents.

In this study, Fe-40wt% TiB2 nanocomposite powders were fabricated by two different methods: (1) conventional powder metallurgical process by simple high-energy ball-milling of Fe and TiB2 elemental powders (ex-situ method) and (2) high-energy ball-milling of the powder mixture of (FeB+TiH2) followed by reaction synthesis at high temperature (in-situ method). The ex-situ powder was prepared by planetary ball-milling at 700 rpm for 2 h under an Ar-gas atmosphere. The in-situ powder was prepared under the same milling condition and heat-treated at 900oC for 2 h under flowing argon gas in a tube furnace to form TiB2 particulates through a reaction between FeB and Ti. Both Fe-TiB2 composite powder compacts were sintered by a spark-plasma sintering (SPS) process. Sintering was performed at 1150℃ for the ex-situ powder compact and at 1080℃ for the in-situ powder for 10 minutes under 50 MPa of sintering pressure and 0.1 Pa vacuum for both processes. The heating rate was 50o/min to reach the sintering temperature. Results from analysis of shrinkage and microstructural observation showed that the in-situ composite powder compacts had a homogeneous and fine microstructure compared to the ex-situ preparation, even though the sintered densities were almost the same (99.6 and 99.8% relative density, respectively).