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Research Papers

# Fundamental Study on Laser Interactions With Nanoparticles-Reinforced Metals—Part I: Effect of Nanoparticles on Optical Reflectivity, Specific Heat, and Thermal Conductivity

[+] Author and Article Information
Chao Ma

Department of Mechanical and
Aerospace Engineering,
University of California,
Los Angeles, CA 90095
e-mail: machao@ucla.edu

Jingzhou Zhao

Department of Mechanical and
Aerospace Engineering,
University of California,
Los Angeles, CA 90095
e-mail: jingzhou.zhao@ucla.edu

Chezheng Cao

Department of Mechanical and
Aerospace Engineering,
University of California,
Los Angeles, CA 90095
e-mail: cheercao@ucla.edu

Ting-Chiang Lin

Department of Mechanical and
Aerospace Engineering,
University of California,
Los Angeles, CA 90095
e-mail: jasonlin77830@ucla.edu

Xiaochun Li

Fellow ASME
Professor
Department of Mechanical and
Aerospace Engineering,
University of California,
Los Angeles, CA 90095
e-mail: xcli@seas.ucla.edu

Manuscript received October 17, 2015; final manuscript received April 1, 2016; published online June 24, 2016. Assoc. Editor: Hongqiang Chen.

J. Manuf. Sci. Eng 138(12), 121001 (Jun 24, 2016) (7 pages) Paper No: MANU-15-1520; doi: 10.1115/1.4033392 History: Received October 17, 2015; Revised April 01, 2016

## Abstract

It is of tremendous interest to apply laser to process nanoparticles-reinforced metals for widespread applications. However, little fundamental understanding has been obtained on the underlining physics of laser interactions with nanoparticles-reinforced metals. In this work, fundamental study was carried out to understand the effects of nanoparticles on the optical and thermophysical properties of the base metal, the corresponding heat transfer and melt pool flow processes, and the consequent surface property in laser melting. Part I presents both experimental and theoretical results on the effects of nanoparticles on the optical reflectivity, specific heat, and thermal conductivity. Electrocodeposition was used to produce nickel samples with nanoparticles. Using a power meter, the reflectivity of Ni/Al2O3 (1.8 vol. %) was measured to be 65.8% while pure Ni was at 67.4%, indicating that the Al2O3 nanoparticles did not change the reflectivity substantially. Differential scanning calorimetry was used to determine the heat capacity of the nanocomposites. The specific heat capacities of the Ni/Al2O3 (4.4 vol. %) and Ni/SiC (3.6 vol. %) at room temperature were 0.424 ± 0.013 J/g K and 0.423 ± 0.014 J/g K, respectively, close to that of pure Ni, 0.424 ± 0.008 J/g K. An experimental setup was developed to measure thermal conductivity based on the laser flash method. The thermal conductivities of these Ni/Al2O3 and Ni/SiC nanocomposites at room temperature were 84.1 ± 3.4 W/m K and 87.3 ± 3.4 W/m K, respectively, less than that of pure Ni, 91.7 ± 2.8 W/m K. Theoretical models based on the effective medium approximation theory were also used to predict the heat capacity and thermal conductivity of the nanoparticles-reinforced nickel. The theoretical results match well with the measurements. The knowledge of the optical and thermophysical properties of nanoparticles-reinforced metals would provide valuable insights to understand and control laser processing of metal matrix nanocomposites.

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## Figures

Fig. 1

Process flow for preparation of pure Ni and Ni/Al2O3 nanocomposite samples

Fig. 2

Experimental setup for reflectivity measurement

Fig. 3

Experimental setup for measurements of thermal diffusivity and conductivity

Fig. 4

SEM micrographs of electrocodeposited Ni/Al2O3 surface

Fig. 5

Measurement of reflectivity of silicon wafer

Fig. 6

Measurement of reflectivities of pure Ni and Ni/Al2O3 nanocomposite

Fig. 7

Measured specific heat of Ni, Ni/Al2O3, and Ni/SiC at room temperature

Fig. 8

Measured photodiode signal and temperature

Fig. 9

Thermal conductivity of pure Ni, Ni/Al2O3, and Ni/SiC at room temperature

Fig. 10

Heat capacities of Ni, Al2O3, and SiC from literature

Fig. 11

Predicted heat capacities of Ni/Al2O3 and Ni/SiC in comparison with that of Ni

Fig. 12

Predicted thermal conductivity of Ni/Al2O3 as a function of nanoparticle size at a fraction of 4.4 vol. %

Fig. 13

Predicted thermal conductivity of Ni/Al2O3 as a function of nanoparticle fraction at a radius of 25 nm

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