Microstructure characterization and modeling the

Microstructure characterization and modeling the mechanical behavior of HVOF sprayed WC–CoCr coatings Yazid FIZI, Yamina MEBDOUA, Hadj LAHMAR, Rachid LAKHDARI Centre de Développement des Technologies Avancées CDTA Algeria 7th Rencontres Internationales sur la Projection Thermique 9th to 11th December 2015 Limoges France

Abstract To simulate the behavior of thermal spray coatings, several finite elements models were developed using OOF and ABAQUS® software. Finite element meshes are therefore constructed on SEM micrographs of high velocity oxygen-fuel (HVOF) sprayed hardmetals (WC10Co 4Cr), employed as case studies. The first model identifies the plastic properties using an inverse identification based on instrumented indentation test. The second model uses a high-magnification micrographs to simulate the uniaxial tensile test. At the macro-scale, another finite element model was also developed in order to simulate the three-point bending test. Comparison between the experimental results and numerical simulations obtained from finite element methods will help us to demonstrate how microstructure-based finite element modelling procedures can be applied to the prediction of the mechanical behavior of thermal spray coatings.

Three point bending test Simulated P-h curve

Experimental P-h curve

Define an objective function as the nimization of : ( )= ∑

HVOF sprayed WC–10Co 4Cr coatings

2



−

Compare computed FE load-displacement curve to experimental curve and check convergence

Composite coating

No

Yes Write results and Stop WC-CoCr spray powders -45 +15µ size

Application of inverse analysis

Initial material parameters: , K, n

L 1400 Test 1 Test 2 Test 3 Test 4 Test 5

1200 1000

Load (N)

5

Modify the values of material parameters

Introduction

1

In the present study, a combination of optical microscopy and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis was used to evaluate the microstructural characteristics of the sprayed hardmetals coating. The elastic-plastic behavior of the coating was identified using instrumented indentation experiments combined to finite elements analysis and according to Hollomon Model.

800 600 400 200 0

0

0.2

0.4

0.6 0.8 Dis placement (mm)

1

1.2

1.4

6

Tensile test simulation ASTM C633-79

7

Toughness of Deposit: eXtended Finite Element Von-Mises stress Crack front Method Failure stress

HVOF Process

Microstructure characterization

3

 

 Wc  W C 2

Intensity (u.a)

 Co  Identified phase

 





  20

30

  40









 

50

60

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90

SEM images of the coating



XRD analysis and mapping of composite coating

Hardness test Hardness HV

Sectional view Evolution of microhardness (HV0.2) as the function of distance from the substrate for as-sprayed coating

FE model for CT25 specimen

3D modeling of interfacial indentation

8

Comparison between experimental and simulation data for indentation 6

Displacement (µm)

Experiment FEA-3D

5

20N

Indentation load (N)

1N

Distribution of stress around the crack

4 3 2 1

Interfacial indentation

4

Microstructure-based FE modelling ɛ=0.2%

WC CDTA

Stress distrubition σyy

CoCr Matrix

E~530GPa

0

9

0

1

2

3 4 Indentation depth (µm)

Conclusion

5

6

7

Contours of the von-Mises Stress

This Work showed a examples demonstrating how microstructure-based finite element modeling procedures can be applied to prediction of the mechanical behavior of thermal spray coatings, with particular reference to HVOF-sprayed hardmetals. The elastic-plastic properties were determined using a non-linear optimization approach based on micro-indentation measurements, finite elements method and inverse analysis technique. The optimized behavior law is then used to simulate the adhesion , double-torsion and indentation interfacial test.

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