Detonation Gun Process Research Articles

Microwave-Assisted Post-processing of Detonation Gun-Sprayed Coatings for Better Slurry and Cavitation Erosion Resistance

Slurry and cavitation erosion often limits the durability of many fluid machines such as hydroturbines, pumps, and propellers. Despite good resistance against slurry erosion, thermal spray coatings generally exhibit poor resistance against cavitation erosion. The performance of thermal spray coatings under cavitation erosion is limited by the presence of defects such as pores, splat boundaries, and limited adhesion with the substrate. In the present work, we performed post-processing of the WC-10Co-4Cr and Ni coatings deposited using the detonation gun process. For post-processing, microwave technique was used owing to its capability for atomic-level heating. The microstructural characterization of the as-sprayed and post-processed coatings showed significant homogenization for the latter. Compared to the typical lamellar structure of as-sprayed, the processed samples exhibited a columnar structure with metallurgical bonding with the substrate. The mechanical properties of the coatings were significantly improved after post-processing owing to the elimination of splat boundaries and pores which significantly enhanced the cavitation and slurry erosion resistance. Post-processed coatings showed at least ten times higher resistance to cavitation erosion. The slurry erosion resistance of the coatings also improved up to three times depending upon the impingement angle. A significant difference in the erosion mechanism was also observed after post-processing.

Study of High-Temperature Corrosion Behavior of D-Gun Spray Coatings on ASTM-SA213, T-11 Steel in Molten Salt Environment

Alloys and metals get corroded when exposed to high temperature in air or in actual boiler environment in thermal plants. In the present study, a Ni-20Cr coating was deposited by detonation gun process on ASTM–AS-213, T-11 boiler steel. Cyclic corrosion studies were carried out in molten salt environment at 900°C for 50 cycles. Each cycle consist of 1 hour heating in Silicon carbide tube furnace followed by 20 minutes cooling in air. The kinetics of weight gain or loss was measured after each cycle and visually examined, the surface studies of the exposed samples were characterized by SEM/EDS and XRD analysis. The results obtained showed the better performance of Ni-20Cr coated T-11 boiler steels than the uncoated T-11 boiler steel.© 2014 The Authors. Elsevier Ltd. All rights reserved.Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Materials Processing and Characterization.

Surface Engineering Analysis of D-Gun Sprayed Cermet Coating in Aggressive Environment

Material degradation due to hot corrosion is a common problem in many engineering system, including coal fired turbines, valves and boiler tubes leading to huge economy losses. Detonation Gun process is a novel coating deposition process among the other thermal spray processes due to its very low porosity, strong adhesion to substrates, high cohesive strength and high hardness. In the present investigation, D-Gun process has been used to deposit Cr3C2–25NiCr coating on 23/8N Nitronic steel. The oxidation behavior of D-Gun sprayed Cr3C2–25NiCr coatings subjected to high temperature (700°C) in actual coal fired boiler for 1000 hours has been carried out in the present work. X-ray diffraction, Field emission–scanning electron microscope technique was used to analyze the scales formed on the surface of the oxidized samples. High volume fraction of carbides contributed for the higher microhardness of the coating (970HV). No microspalling of the scales were showed by the coated specimen. The scale remained intact and adherent to the substrate. The development of protective oxide scale of chromium, nickel and spinel of nickel and chromium have contributed the better oxidation resistance for coated specimen. The Cr3C2-25 NiCr coating imparted better hot corrosion resistance than the uncoated one in the given environment.

Particle Acceleration in a High Enthalpy Nozzle Flow with a Modified Detonation Gun

The quality of thermal sprayed coatings depends on many factors which have been investigated and are still in scientific focus. Mostly, the coating material is inserted into the spray device as solid powder. The particle condition during the spray process has a strong effect on coating quality. In some cases, higher particle impact energy leads to improved coating quality. Therefore, a computer-controlled detonation gun based spraying device has been designed and tested to obtain particle velocities over 1200 m/s. The device is able to be operated in two modes based on different flow-physical principles. In one mode, the device functions like a conventional detonation gun in which the powder is accelerated in a blast wave. In the other mode, an extension with a nozzle transforms the detonation gun process into an intermittent shock tunnel process in which the particles are accelerated in a high enthalpy nozzle flow with high reservoir conditions. Presented are experimental results of the operation with nozzle in which the device generates very high particle velocities up to a frequency of 5 Hz. A variable particle injection system allows injection of the powder at any point along the nozzle axis to control particle temperature and velocity. A hydrogen/oxygen mixture is used in the experiments. Operation performance and nozzle outflow are characterized by time resolved pressure measurements. The particle conditions inside the nozzle and in the nozzle exit plane are calculated with a quasi-one-dimensional WENO-code of high order. For the experiments, particle velocity is obtained by particle image velocimetry, and particle concentration is qualitatively determined by a laser extinction method. The powders used are WC-Co(88/12), NiCr(80/20), Al2O3, and Cu. Different substrate/powder combinations for varying particle injection positions have been investigated by light microscopy and measurements of microhardness.

Optimization of Abrasive wear Characteristics of Tungsten Carbide and Chromium Carbide based coating on Mild Steel deposited by Detonation Gun Process using Taguchi Method

Mild steel forms the basis of almost every industry, the present industrial system survives on the soul of some of the basic elements and their systematic properties like strength, toughness, hardness, failure stress etc. Along with these major properties some properties are such they may seem to be less important and not considered but for the long run they play major part in the life and working of material. One such property is the abrasive wear property of the material. Though the abrasion in one run of the system looks very negligible and not considerate but when the mechanism of abrasion is taken into consideration on the large machinery like the turbines and turbo propellers this becomes very important and its consideration forms the major study part. The present study generally works on the abrasion wear often called as a three body wear system on mild steel and the coating of tungsten carbide and chromium carbide on it ,which is deposited by the detonation gun process, the testing is performed on the dry rubber wheel abrasion testing machine at various varying parameter like the velocity of the rubber wheel, normal load applied on the machine and the coating component itself ,hence for the above a design of experiment matrix is formed, the solution of the matrix is done using the Taguchi method of optimization. This method not only determines the significant interactions and respective factors but also determines the significant interaction factor combination. Finally, genetic algorithm, a very popular evolutionary approach, is employed to optimize the factor settings for minimum specific wear rate under specific experimental conditions. The experimentation described is expected to be highly useful in the various large scale assemblies like the turbine assembly (the rotor part), and also in the areas such as construction aerospace sector. Mild steel is the most common form of steel. It is not brittle, it’s really hard, and it is cheap. It is often used when large amounts of steel are needed. Mild steel is a carbon steel typically with a maximum of 0.25% Carbon and 0.4%-0.7% manganese, 0.1%-0.5% Silicon and some traces of other elements such as phosphorous, it may also contain lead (free cutting mild steel) or sulphur (again free cutting steel called re-sulphurised mild steel). Mild steel (a so-called carbon steel) is a general term for a range of low carbon (a maximum of about 0.3%) steels[1] that have good strength and can be bent, worked or can be welded into an endless variety of shapes for uses from vehicles (like cars and ships) to building materialscontains a small amount of carbon. Due to the high usage of this in the industry it becomes very important for us to consider the wear property if it.Mild steel has always being area of interest and several methods are used to increase the structural and mechanical properties of it but no studies have so far being conducted on the abrasion wear[2] that is three body wear behavior for mild steel. Three body wear is generally defined as the property of erosion or abrading the metal surface by the action of a medium between the abrading surface ,generally direct contact erosion of the metal does not take place. Several methods and practices are utilized in the present scenario to increase the property of mild steel one such method is the thermal spraying[3-6] process where the layer of

A study on phase stability observed in as sprayed Alumina-13 wt.% Titania coatings grown by detonation gun and plasma spraying on low alloy steel substrates

AT-13 wt.% type powders, depending on the process used for spraying has shown variable type of resultant phases in the as sprayed conditions. In a detonation gun process it appears that freezing of the molten plume with the same composition as the liquid was possible, in contrast to this in a typical plasma spraying process preferential evaporation and phase separation of the solute from the molten plume was prevalent. These variations to the solidification paths has resulted in a totally metastable γ phase in the former process and in the latter process heterogeneous nucleation of α phase in addition to the normal nucleation of metastable γ phase was observed. In all cases the titanium present in the solute appears to be merely trapped in the metastable γ phase and a newer type of metastable “X” phase which has high solubility for titanium, as reported in the literature, did not form in any of the processes studied. The imposed rapid solidification condition had caused all the phases stabilized to be of nanocrystalline sizes which could be verified by Hall–Williamson analysis. Owing to the solute trapping of titanium the lattice of metastable γ phase was severely micro strained and titanium cation was nearly insoluble in α phase.

Tribological coatings for liquid metal and irradiation environments

Several metallurgical coatings have been developed that provide good tribological performances in high-temperature liquid sodium and that are relatively unaffected by neutron fluences to 6 × 1022 n/cm2 (E >0.1 MeV). The coatings that have consistently provided the best tribological performance have been the nickel aluminide diffusion coatings created by the pack cementation process, chromium carbide or Tribaloy 700 (a nickelbase hardfacing alloy) applied by the detonation-gun process, and chromium carbide and other hardfacing materials applied by the electro-spark deposition process. The latter process is a relatively recent development for nuclear applications and is expected to find wide usage. Other coating processes, such as plasma-spray coating, sputtering, and chemical vapor deposition, were candidates for use on various components, but the coatings did not pass the required qualification tests or were not economically competitive. The advantages and limitations of the three selected processes are discussed, the tribological performance of the coatings is reviewed, and representative applications and their performance requirements are described.

Detonation Gun Coatings

The detonation gun process allows the utilization of a large number of compositions and structures as coatings tailored to provide superior performance in a given environment. In addition, this coating process requires no excessive thermal exposure of a component and, hence, can be applied to substrates that have been heat treated to the required strength levels before coating. These coatings can also be stripped and reapplied many times allowing repeated use of a component with consequent savings. In short, this type of coating frequently results in lower initial cost, longer service life, and an opportunity for repair/overhaul rather than replacement.

Factors affecting the performances of sprayed chromium carbide coatings for gas-cooled reactor heat exchangers

Abstract This paper discusses some important factors to be considered for using sprayed coatings in gas-cooled reactor heat exchangers. These factors include (a) high temperature gaseous corrosion, (b) thermal stability of coatings, (c) metallurgical compatibility between the coating and the substrate and (d) effects of the coating on the mechanical properties of the substrate alloy. The wear properties of the coatings are also important but will not be discussed in this paper. The coatings evaluated were Cr3C2(NiCr) and Cr23C6(NiCr) applied by either the plasma arc or the detonation gun process. Two types of gaseous corrosion can cause coatings to spall from the substrate material in high temperature gas-cooled reactor (HTGR) helium environments. In the high temperature sections of heat exchangers, which are made of alloy 800H because of its excellent strength properties at elevated temperatures, preferential oxidation of the substrate alloy 800H at the coating-substrate interface can occur at temperatures above 649 °C (1200 °F). The lateral growth of interfacial oxides can eventually spall the coating from the substrate. In the low temperature section of the heat exchanger made of 2 1 4 Cr−1 Mo steel, the exposure of the coated steel to the HTGR helium in the temperature range 300–600 °C can lead to carbon deposition at the coating-substrate interface resulting in spallation of the coating. Furthermore, during high temperature exposure, structural changes of carbide phases in the coating, accompanied by volume changes, can further promote coating spallation. In HTGR helium environments, the structural change of chromium carbide is expected to occur in the following manner: Cr3C2→Cr7C3→Cr23C6 Accordingly, Cr23C6-based coatings are preferred to Cr3C2-based coatings for high temperature applications. A limited degree of interdiffusion was observed between the coating and the substrate after thermal aging. Interdiffusion occurred mainly between the Ni-Cr phase and the substrate. No Kirkendall-type voids were observed as a result of this interdiffusion.

Evaluation of sprayed chromium carbide coatings for gas-cooled reactor applications

Sprayed chromium carbide-Nichrome coatings are candidates for the protection of faying and sliding surfaces of critical components of gas-cooled reactors from friction and wear damage. These coatings must provide protection throughout the reactor lifetime under high temperature exposure conditions. Extensive evaluation work to characterize the coatings is under way. The work includes studies of (1) their friction and wear behavior in helium, (2) the stability of the coatings in a low oxygen potential helium environment, (3) the impure helium corrosion of coated specimens and (4) the effect of the coatings on the mechanical properties of the substrate alloy. Much of the work reported is on the evaluation of plasma-sprayed coatings. However, a brief discussion of the behavior of coatings applied by the detonation gun process and by high energy plasma gun processes is also included.

Wear resistant coatings for reactor components in liquid sodium environments

Rubbing surfaces of critical components for the coming generation of the nation's liquid–metal-cooled fast-breeder reactors must withstand severe environments of high temperature, liquid–metal corrosion, and nuclear irradiation. For some component requirements, the use of the better known bearing materials and hardfacings has been shown to be inadequate or impractical. For several applications, bulk (> 25-μ thick) coatings have provided the only successful solution to friction problems in high-temperature sodium. Coating processes that have been or are being evaluated include plasma spray, detonation gun, spark-discharge, sputtering, and diffusion coating processes. Testing included friction and wear tests in up to 650 °C sodium, sodium corrosion tests for up to one year, thermal cycling, bond strength tests, and irradiation tests in a fast reactor. For one particularly severe application, a specially modified commercial coating of chromium carbide in a 15 vol% nichrome binder, applied by a commercial detonation gun process, has so far been found to be most acceptable in meeting the friction, corrosion, and irradiation damage criteria. Much of the test data reported is on this coating and its antecedent modifications.