Microsoft Word - ETASR_V13_N2_pp10367-10371 Engineering, Technology & Applied Science Research Vol. 13, No. 2, 2023, 10367-10371 10367 www.etasr.com Vu: Prediction of the Adhesion Strength of Coating in Plasma Spray Deposition Prediction of the Adhesion Strength of Coating in Plasma Spray Deposition Duong Vu School of Engineering Technology, Duy Tan University, Vietnam duongvuaustralia@gmail.com (corresponding author) Received: 8 January 2023 | Revised: 21 January 2023 and 28 January 2023 | Accepted: 4 February 2023 ABSTRACT The goal of this work is to validate the existing plasma spray mathematical models, using a calculation method and the comparison with experimental data, in order to determine their validity. A preliminary evaluation of the adhesion based on the velocity and temperature of the particles is useful to be calculated by using the mathematical model. Given the thermal-physical properties and chemical composition of a Fe- based amorphous X-5 powder, a modified model was suggested. For comparison, a series of experiments using plasma spraying of the X-5 powder were conducted. The significance of the current study consists of the model validation by using the data of the plasma spraying of the Fe-based amorphous material as a potential substitution for saving production costs by using ordinary air as the plasma generation gas. The findings show the discrepancy between the models and the experimental results. The prediction of adhesion using the mathematical models does not cover essential parameters such as the enthalpy of the particle stream. It is necessary to improve the mathematical models, including the modified one, based on the experiment results, with different pairs of particles and substrate materials. The proposed formula is applicable during the preliminary design of the spray process and the development of a new torch construction. Keywords-adhesion; coating; particle velocity; particle temperature; validity; prediction I. INTRODUCTION Plasma spray deposition is an additive manufacturing technology whose application range extends beyond the traditional thermal spraying approach, including the plasma spraying approach, which relies heavily on melting. The plasma energy encourages the nitriding process to modify the structure and mechanical properties of the surface, but the temperature and chemical process prevail [1]. Many engineers and researchers have worked to produce thermal spray technology without melting, and the velocity of the particles is the primary driver in creating the deposition. Cold Spraying (CS) is the term for this procedure. Particles stick to and deposit onto a substrate in CS without melting, allowing functional coatings to be deposited. In recent years, technologies that use particle kinetic energy in addition to thermal energy, such as High-Velocity Oxy-Fuel (HVOF) flame spraying and thermal spraying, have been developed. The most common example of these new approaches is the CS method. The natural oxide film on the surface is damaged by repeated particle impacts during the activation phase, known as incubation, and an increase in chemical activity due to the creation of the nascent surface is critical to adhesion. Due to the quick impact of the solid particles, it was inferred that the contribution of atomic diffusion to adhesion is low. Plastic deformation occurs when the substrate material and particles undergo explosive bonding upon particle contact, undulating in a wavy pattern, and layers are created by mixing in tiny interfacial areas [2]. During this collision, however, severe plastic deformation caused by particle impact might dramatically affect the bonding process, causing shear instability. The natural oxide films on the particle and substrate are removed, and the surface is activated, resulting in the formation of a strong sticky area. The particle and substrate constituent parts are in intimate contact, as shown in TEM images, in the absence of inclusions such as the oxide at the adhering interface. As a result, surface activation is a critical element in particle adhesion mechanisms, and the CS technique's massive plastic deformation following impact significantly adds to this surface activation. Figure 1 depicts a method in which plastic deformation is triggered by the kinetic energy released by the collision of CS material particles. A material jet in the outer peripheral direction caused by thermal shear instability breaks and eliminates the particles and oxide coating on the substrate surface. A new chemically active surface is revealed, and the new surfaces are strongly connected to each another. In recent publications, some mathematical models describing the plastic deformation have been introduced, including the thermal spraying when the heating particles deposit on the substrate. However, the main disadvantage of these models is the lack of technological parameters, which limits their application in the prediction of adhesion strength in coatings as a significant criterion for deposition evaluation. In Engineering, Technology & Applied Science Research Vol. 13, No. 2, 2023, 10367-10371 10368 www.etasr.com Vu: Prediction of the Adhesion Strength of Coating in Plasma Spray Deposition this context, a new modified mathematical model dealing with the sufficient prediction of adhesion strength must be introduced and validated. In the event of a disagreement, the empirical formula should be considered the most important recommendation. In this paper, the digital method for the calculation of the predicted adhesion by the digital own program PROGX100 is described and the amorphous powder X-5 is proposed for the plasma spraying, while in the experimental part the relationships between enthalpy and air flow rate and between adhesion, power of plasma, and velocity of particles were specified, while some significant recommendations and the direction of future studies are presented. II. METHODOLOGY Significant plastic deformation was found at the interface edge due to the presence or absence of the remaining oxide film, and fracture and strong bonding were observed due to the ease with which the oxide film was removed. On the other hand, the quantity of plastic deformation in the area of the particle center was tiny hence the oxide film persisted even after the impact, generating a very weak bond. According to [3], in addition to substrate hardness, particle velocity and spray angle can influence deformation behavior and the ultimate state of the oxide film. The equation in [1] justifying the role of the critical velocity (Vcr) as the condition governing the feasibility of bonding was impacted by a rise in the local temperature beyond the melting point. 667 14 0.08 0.1 0.4cr p m u PiV T T          (1) where ρp is the density of the particle, Tm is the melting point of the particle, σu is the tensile strength of the particle, and TPi is the initial temperature of the particle. Due to adiabatic deformation, when particles hit at high speeds, the particle temperature quickly rises to the melting point. During the collision, much of the kinetic energy of the particle will be transformed into heat, encouraging plastic deformation. Softening is expected to produce particles that constitute the material jets. The Johnson-Cook (JC) model [4] is widely used in manufacturing to simulate high-speed deformation and can be used for high-velocity particle spraying [5, 6]: � = � A + B × �� � � × 1 + × �� × �� ��� � � × �1 − � � � ������ � ���� � � (2) where σ is the flow stress, A, B, C, m, and n are the material constants, �� � is the plastic strain, ��� and ��! are the actual strain and the reference strain rates, respectively, and T, Tm, and Tref are the actual, melting, and reference temperatures, respectively. The restriction of models (1) and (2) is the practical reference because, in the thermal spray, the activation energy and temperature of the contacting surface at the time of the impact must prevail. In this regard, the Kudinov V.V. model should be examined since it simplifies the computation of adhesion in terms of its prediction for designing the thermal process [7]: " #(%) "% = '() − ((*)+×v×exp − ,-. × �/ �×exp 0 . � (3) where Ea is the activation energy in this case, v is the frequency of the atoms own oscillation, Tk is the contact's absolute temperature, N0 is the number of atoms on the surface of the substrate or particle that make up the mutual physical contact, N(t) denotes the number of atoms energized during the activation time t, S denotes the activation entropy in the chemical reaction zone, and k is the Boltzmann constant. Since the predominant metal has a BCC or FCC crystal structure, (3) will be transferred to the new type: " #(%) "% = '() − ((*)+×v×exp − ,-. × �/ � (4) The rate of the chemical interaction on the phase boundary is defined by the relative adhesion of the particle with the substrate: 1 (%)1�-2 = #(%)#3 (5) where � (*) is the adhesion resulting for duration t, ��45 is the maximum adhesion obtaining for the entire cycle of the spraying. The influence of the particle velocity on the adhesion can be calculated according to [8]: σ = V 2 ×ρ, where V is the particle velocity and ρ is the density of the particle material. By the integration, (4) will be changed as follows: 1 (%)1�-2 = 1 – exp 6− 7 ×%89: ;-/ × ?@AB@× C4D (7) For most of the materials, E = 1013×c-1; h = 0.1×d, where d is the diameter of the particle and Ea ≈ 1.35 – 1.65 eV. Equation (7) describes the change in adhesion depending on the activated temperature during the collision of the particle with the substrate. On the other side, the quantity Tk can be calculated with respect to the known equation [7]: Tk(t) = T0 + Tk 0 ; Tk 0 = ( �� F ��)×G�G�H I(A) (8) where h is the height of the solidified particle in the collision on the substrate, t0 is the time during which the particle is solidified and the constant contact temperature Tk is activated, T0 is the initial temperature of the substrate, and a1 is the coefficient of the thermal conductivity of the particle. α = f(J�, KL) and α varies in 0 - 1 depending on J� and KL. J� = KDKL × M4L4D; KL= N ×��C.PP ×Q (9) where J� is the criterion of the thermal activity of the particle in relation to the substrate, KL is the criterion defining the latent heat of fusion of particle material, λ1 and λ2 are the coefficients of the thermal conductivity of the particle and the substrate, respectively, a1 and a2 are the coefficients of the thermal diffusivity of the particle and substrate, L is the latent heat of the fusion, c is the heat capacity of the particle, Tm is the Engineering, Technology & Applied Science Research Vol. 13, No. 2, 2023, 10367-10371 10369 www.etasr.com Vu: Prediction of the Adhesion Strength of Coating in Plasma Spray Deposition melting point of the particle material, F(α) is the integral of the probability, and α = f(J�, KL), the root of the function. J� + F(α) = KL R�SLA (10) α can be defined by using the φ-α diagram [7], where α is the abscissa of the intersection between the two curves [7]:  = J� + F() = ( J�; ) (11) T = KL × e-S2A = T (KL; α) (12) The temperature during the solidification of the particle is defined by [7], with T1 being the temperature of the particle: Tk = �D  G� G�H I(A) (13) Given the properties of the particle and the substrate materials, the prediction of the change in adhesion in thermal spraying can be calculated using (6)-(9). The second method is to use (10) and (11) to find the root of the contacting temperature given J� and KL. Since the adhesion depends not only on the heating effect, but also on the plastic deformation during the collision of the melting particle on the substrate, it is useful to consider a modified model for the prediction of changes in the adhesion: 1 (%)1�-2 = 1 – exp V− 7 ×%89:W ×( XFY ×Z;)[ ×S ×