Research on Laser Cladding Co-Based Alloy on the Surface of Vermicular Graphite Cast Iron

To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), energy spectroscopy (EDS), X-ray diffractometer (XRD), electrochemical workstation, and friction wear equipment. The results show that the average hardness of the molten layer of Ni and Co-based composite cladding layer is 504 HV0.5, which is 0.64 times that of the Co-based cladding layer due to the combined factors of Ni-Cr-Fe equivalent to the dilution of the Ni-based cladding layer to the Co-based cladding layer. Due to the potential difference of the Ni, Cr, and Co elements on the surface of the cladding layer, the self-corrosion potential of the Ni and Co-based composite cladding layer is 1.08 times that of the Co-based cladding layer, and the self-corrosion current density is 0.51 times. Laser cladding Co-based cladding layer has high corrosion resistance. Under the influence of plastic deformation and oxidative wear of the cladding layer of the Ni and Co-based composite cladding layer, the wear amount of the cladding layer of the Ni and Co-based composite cladding layer is less.

Numerical Simulation of Convex Shape Beam Spot on Stress Field of Plasma-sprayed MCrAlY Coating During Laser Cladding Process

In order to reduce the thermal stress at clad layer and further reduce the crack generation in the laser cladding process, a method of controlling the cracks at clad layer by changing the laser energy density was proposed. The comparative thermal-mechanical coupling finite element analysis was conducted for the uniform rectangular spot and convex shape beam spot cladding processes on plasma-sprayed MCrAlY coating through the numerical simulation method based on the ANSYS software. The results show that the rapid heating and cooling characteristics, which are typical in laser processing, are manifested in the cladding process using the uniform rectangular spot, and the convex shape spot can exert the preheating and slow cooling effects to a certain extent, so as to reduce the temperature gradient of the cladding zone and non-cladding zone. In addition, on the precondition of equivalent cladding effect, the thermal stress at the clad layer is also low, so the cracking tendency of the clad layer can be effectively mitigated. Relative to the laser beam shaped diffractive optical element special for design and manufacturing, superposing two uniform rectangular spots with different sizes and energy densities is a simpler and more effective method of acquiring the convex shape spot.

Method of investigation of local corrosion processes on samples from clad steel

The article describes a method developed to evaluate the mechanism of local corrosion processes on the surface of a clad layer of steel specimens, which makes it possible to identify the difference in electrode potentials in artificially created holes. As a result of the study it was found that in a corrosive medium containing Cl- and S2O32- ions, the diffusion of oxidants into a hole of smaller diameter is difficult, which causes a large potential difference between the wall of the hole and its bottom. This process contributes to the development of local electrochemical corrosion.

SELECTION OF RATIONAL POLISHING MODES FOR CLADDED CHROME COATINGS

As a result of experimental and statistical modeling, dependencies were obtained that establish the effect of polishing modes (the number of passes of the polishing wheel, the value of the wheel tightness) on the roughness and thickness of the chrome coating obtained by the method of deformation cladding with a flexible tool. It was found that within the selected intervals of variation of the factors, an increase in the tightness of the polishing wheel and the number of passes of the wheel leads to a decrease in both the parameter of the roughness Ra and the thickness of the coating, however, with different degrees of intensity. The number of passes of the polishing wheel has a decisive effect on the value of the surface roughness of the clad layer after polishing. The effect of polishing modes on the thickness of the cladded coating is more complex, since it is demonstrated both in the individual comparable influence of both factors and in their interaction. The optimal modes of polishing of hydraulic cylinder rods subjected to chromium plating by the method of deformation cladding with a flexible tool have been determined. After the experimental check in the conditions of JSC “Minsk Automated Lines Plant named after P.M. Masherov” (Republic of Belarus), the established technological modes of polishing were added to the technological process of chromium plating of rods. It confirms the effectiveness of using the calculated dependencies.

The Formability and Elongation of Aluminum Alloys AA5083 and AA3003 for Micro-Truss Sandwiches Manufacturing

The development in the manufacturing of micro-truss structures has demonstrated the effectiveness of brazing for assembling these sandwiches, which opens new opportunities for cost-effective and high-quality truss manufacturing. An evolving idea in micro-truss manufacturing is the possibility of forming these structures in different shapes with the aid of elevated temperature. This work investigates the formability and elongation of aluminum alloy sheets typically used for micro-truss manufacturing, namely AA5083 and AA3003. Tensile tests were performed at a temperature in the range of 25-500 ○C and strain rate in the range of 2x10-4 -10-2 s-1. The results showed that the clad layer in AA3003 exhibited an insignificant effect on the formability and elongation of AA3003. The formability of the two alloys was improved significantly with values of m as high as 0.4 and 0.13 for AA5083 and AA3003 at 500 °C. While the elongation of both AA5083 and AA3003 was improved at a higher temperature, the elongation of AA5083 was inversely related to strain rate. It was concluded that the higher the temperature is the better the formability and elongation of the two alloys but at the expense of work hardening. This suggests a trade-off situation between formability and strength.

Characteristics Regarding Lift-Off Intersection of Pulse-Modulation Eddy Current Signals for Evaluation of Hidden Thickness Loss in Cladded Conductors

The cladded conductor is broadly utilized in engineering fields, such as aerospace, energy, and petrochemical; however, it is vulnerable to thickness loss occurring in the clad layer and nonconductive protection coating due to abrasive and corrosive environments. Such a flaw severely undermines the integrity and safety of the mechanical structures. Therefore, evaluating the thickness loss hidden inside cladded conductors via reliable nondestructive evaluation techniques is imperative. This paper intensively investigates the pulse-modulation eddy current technique (PMEC) for the assessment of thickness loss in a cladded conductor. An analytical model of the ferrite-cored probe is established for analyzing PMEC signals and characteristics of lift-off intersection (LOI) in testing signals. Experiments are conducted for evaluation of the thickness loss in cladded conductors. An inverse scheme based on LOI for estimation of the thickness-loss depth is proposed and further verified. Through simulations and experiments, it is found that the influences of the thickness loss in the clad layer and protective coating on the PMEC signals can be decoupled in virtue of the LOI characteristics. Based on LOI, the hidden thickness loss can be efficiently evaluated without much of a reduction in accuracy by using the PMEC probe for dedicated inspection of the cladded conductor.

ДЕФОРМАЦИОННЫЙ РЕЛЬЕФ И ДЕСТРУКЦИЯ ПОВЕРХНОСТИ КАК ПОКАЗАТЕЛИ УСТАЛОСТНОЙ ПОВРЕЖДЕННОСТИ ПЛАКИРОВАННОГО АЛЮМИНИЕВОГО СПЛАВА

The article presents the results of the study of changes in the state of the structural alloy D16AT surface with the operating time at various stress levels. The state of the surface of the material was monitored by an interference nanoprofiler. The main feature of the D16AT alloy is that to protect against corrosion, the material is coated on both sides with a thin layer of clad, the thickness of which is about 5 % of the sheet total thickness. During loading, the deformation of the cladding layer and the base material due to the existing difference in the yield strength values differs significantly. Such a composition of inextricably bound materials will contribute to the intensification of plastic deformation of the surface layer. During cyclic loading, areas of plastically deformed material are formed and developed on the surface of a clad aluminum alloy with a special representation of the surface relief caused by dislocation mechanisms (steps and slip bands, extrusion, intrusion etc.). Quantitative indicators of deformation relief (DR) are the area and perimeter of plastic-deformed areas, their fractal characteristics and plastic deformation of the surface. These parameters can act as indicators of the alloy fatigue damage, but it is hard to identify the boundary state that is the fatigue crack initiation. Such a diagnostic parameter is the destruction of the clad layer to determine in order are used basic indicators of DR. Destruction (increase in the volume of the clad layer) is physically objective that is associated with an increase in surface area during the formation and extended of DR. Destruction can be considered as the main factor in the fatal destruction of clad aluminum alloys. It is shown that when saturated with a deformation relief, approximately 25 ... 30 % of the total surface area of the destruction of the clad layer increases abruptly due to the change in the nature of the plastic deformation of the surface that is an increase in the growth of its plane at high saturation values. This saturation value can be used as a diagnostic indicator of the initial fatigue cracks initiation.