Journal of Materials Science

, Volume 47, Issue 1, pp 184–198

Interfacial heating during low-pressure cold-gas dynamic spraying of aluminum coatings

Article

DOI: 10.1007/s10853-011-5786-z

Cite this article as:
Dewar, M.P., McDonald, A.G. & Gerlich, A.P. J Mater Sci (2012) 47: 184. doi:10.1007/s10853-011-5786-z

Abstract

Low-pressure cold spraying was used to deposit aluminum particles (~25 μm diameter) on to low carbon steel, and the particle–particle interactions of the aluminum coating were analyzed. A simplified energy conservation model was developed to estimate the temperature at the interface of the deformed particle during deposition of the powder. The Johnson–Cook model was used to calculate the particle flow stress, which was used to estimate the total energy dissipated via plastic deformation during impact and spreading of the particle. Microstructural analysis was conducted to show that plastic deformation occurred mainly at the interfacial regions of the deformed particles. By coupling microstructural observations of the cold-sprayed particles with the energy conservation model, it was found that the interface between the aluminum particles contained recrystallized ultra-fine and nanocrystalline grain structures that were likely formed at temperatures above 260 °C, but the majority of particles likely achieved interfacial temperatures which were lower than the melting point of aluminum (660 °C). This suggests that local melting is not likely to dominate the inter-particle bonding mechanism, and the resulting interfacial regions contain ultra-fine grain structures, which significantly contribute to the coating hardness.

List of symbols

A

Yield stress (MPa)

Ap

Projected area normal to gas flow (m2)

As

Surface area of particle (m2)

B

Johnson–Cook strain hardening constant (Pa)

Bi

Biot number

cp

Specific heat capacity (J kg−1 K−1)

C

Johnson–Cook strain rate constant

CD

Drag coefficient

dp

Particle diameter (m)

dsplat

Splat diameter, after spreading (m)

Dnozzle

Nozzle diameter (m)

Ek

Kinetic energy (J)

Ep

Plastic deformation energy (J)

h

Heat transfer coefficient (W m−2 K−1)

k

Thermal conductivity (W m−1 K−1)

kg

Thermal conductivity of free stream carrier gas (W m−1 K−1)

Lx

Distance traveled by particle (m)

mp

Particle mass (kg)

M

Mach number

n

Hardening exponent

Nu

Nusselt number, Nu = hdp/kg

Pg

Absolute gas pressure (Pa)

Pr

Prandtl number, Pr = cpμ/kg

r

Recovery factor

R

Gas constant (kJ kg−1 K−1)

\( Re_{{d_{\text{p}} }} \)

Reynolds number based on particle diameter, \( Re_{{d_{\text{p}} }} = \rho_{\text{g}} (V_{\text{g}} - V_{\text{p}} )d_{\text{p}} /\mu_{\text{g}} \)

tc

Contact time (s)

ti

Time at iteration i

tx

Time traveled by particle (s)

Taw

Adiabatic-wall temperature (K)

Tg

Free stream carrier gas temperature (K)

Ti

Temperature at increment i (K)

Tinitial

Initial particle temperature prior to impact (K)

Tinterface

Particle–substrate interface temperature (°C)

Tbulk

Temperature in the interior of the particle during deformation (°C)

Tm

Melting temperature (K)

To

Ambient temperature (K)

Tsub

Temperature of substrate (K)

Vg

Carrier gas velocity (m/s)

Vi

Particle velocity at increment i

Vp

Particle velocity (m/s)

X

Nozzle length (m)

Greek symbols

α

Thermal diffusivity (m2s−1)

γ

Specific heat ratio

δ

Lamellae thickness (m)

εf

Final von Mises equivalent strain

εi

Equivalent strain at increment i

εi*

Strain rate at increment i

θ

Non-dimensional interface temperature

μg

Viscosity of free stream carrier gas (kg m−1 s−1)

μs

Viscosity of gas at particle surface (kg m−1 s−1)

μo

Reference viscosity of gas (kg m−1 s−1)

ξ

Non-dimensional particle diameter

ρ

Particle/splat density (kg m−3)

ρg

Gas density (kg m−3)

σ

Von Mises equivalent flow stress (Pa)

Ω

Particle volume (m3)

Ωsplat

Volume of a particle after impact and deformation on the substrate (m3)

Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  1. 1.Department of Chemical and Materials EngineeringUniversity of AlbertaEdmontonCanada
  2. 2.Department of Mechanical EngineeringUniversity of AlbertaEdmontonCanada

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