Surface Repair of Tool Made of 12 Ni Maraging Steel by Laser Cladding of NiCoMo Powder

Surface repair experiments with Nd:YAG coaxial laser cladding of NiCoMo maraging powder were made on specimens from maraging steel (EN 10027-2, mat. no. 1.2799). The influences of different modes of laser-beam guidance with various powder mass flows and with different degrees of overlapping of individual traces on the dilution and the repair area were determined. The micro and macroscopic analyses of microsections of fusion zone (FZ), heat affected zone (HAZ) and through-depth microhardness were analysed after cladding and after subsequent solution and precipitation annealing. The microchemical (EDS) analysis was performed at various depths. The residual stresses in the clad face and in the clad toe were determined and compared, using the hole-drilling method

Effect of pulse laser energy density on TiC cladding of aluminium substrate

U ovom je radu sloj obložen TiC-om proizveden skeniranjem laserom preko prethodno položenog praha TiC-a na aluminijsku podlogu pomoću pulzirajućeg Nd:YAG lasera. Ovisno o efektivnoj gustoći energije na površini uzorka, TiC je položen ili djelomično raspršen u rastaljeni aluminij na površini uzorka. Mikrostruktura je određena pomoću optičkog mikroskopa i SEM/EDS analize. Dubina obloženog sloja i mjerenja mikrotvrdoće određena su na poprečnom presjeku uzoraka oblaganih pomoću lasera. Analizirao se učinak gustoće pulzirajuće energije lasera na dubinu oblaganja sloja, mikrotvrdoću, površinsku hrapavost i valovitost. Eksperimentalna analiza je pokazala da efektivna gustoća energije značajno utječe na hrapavost i valovitost površine obložene TiC-om, ali vrlo malo na mikrotvrdoću obloženog sloja.In this work, TiC cladded layer has been produced by laser scanning over the preplaced TiC powder on aluminium substrate, using a pulse Nd:YAG laser. Depending on the effective energy density at the specimen surface, TiC was deposited or partially dispersed into the melted aluminium at the specimen surface. Microstructure was evaluated using optical microscopy and SEM/EDS analysis. Depth of laser cladded layer and microhardness measurements have been deliberated at the cross-section of laser cladded specimens. Effect of pulse laser energy density on cladding layer depth, microhardness, surface roughness and waviness has been studied. From the experimental analysis it is revealed that effective energy density has a significant effect on the TiC cladded surface roughness and waviness, but very little on microhardness of the cladded layer

Roughness, residual stresses and pitting corrosion effect on shot peened AA 7075

Rad analizira učinak hrapavosti, zaostalih naprezanja i točkaste korozije na sačmarenoj ENAW 7075 aluminijskoj leguri u različitim stanjima. Odgovarajući profil zaostalog naprezanja povećava primjenljivost i trajnost mehaničkih dijelova, podvrgnutih sačmarenju. Točkasta korozija uvelike utječe na starenje konstrukcijskih elemenata izrađenih od aluminijskih legura visoke čvrstoće budući da rupice nastale korozijom dovode do ranijeg stvaranja pukotina zbog zamora materijala pod vlačnim dinamičkim opterećenjem. U svrhu poboljšanja otpornosti materijala na zamor zbog korozije, potrebno je smanjiti naprezanja na rubove pukotina. Da bi se otklonila ili smanjila ta naprezanja, predloženo je sačmarenje. Cilj je istraživanja bio pronaći optimalne parametre sačmarenja aluminijske legure u raznim stanjima precipitacijskog otvrdnjavanja u odnosu na profile zaostalog naprezanja i otpornost na koroziju. Analiza je pokazala da čestice kao što su Al7Cu2Fe i MgZn2 imaju važnu ulogu u točkastoj koroziji te su se nakon sačmarenja smanjili broj i veličina pukotina na površini.The paper deals with the effect of roughness, residual stresses and pitting corrosion on different shot peened (SP) ENAW 7075 aluminium alloy in different states. Suitable residual stress profile increases the applicability and life cycle of mechanical parts, treated by shot peening. Pitting corrosion has a major influence on aging of structural elements made of high strength aluminium alloys as corrosion pits lead to earlier fatigue crack initiation under tensile dynamic loading. In order to improve material resistance to corrosion fatigue it is necessary to reduce pit-tip stresses. To eliminate or reduce pit stresses, shot peening was proposed. The objective of the research was to establish the optimal parameters of the shot peening treatment of the aluminium alloy in different precipitation hardened states with regard to residual stress profiles and corrosion resistance. The analysis indicated that particles such as Al7Cu2Fe and MgZn2 play an important role in pitting corrosion and after SP the number and size of surface pits was reduced

Laser Peening For Improving Metallic Components

Suitable variation of residual stress profiles, fatigue strength and frequently also corrosion resistance of a material, are key requirements to be fulfilled for usability and long life of a vital machine component. Laser Peening (LP) is an innovative surface treatment which was initially developed for the aeronautic industry as the method for the improvement of the fatigue cracking resistance of the turbine spades of an aircraft, such as Falcon F-16 and Rockwell F-22. LP is based on plasma generation, which produces shock impact waves, which, in turn, produce elastoplastic shifts of atomic planes and generation of compressive residual stresses of high gradient [1]. LP has been applied to different types of steels, aluminium and titanium alloys [2]. In practice, technologists and engineers frequently require the introduction of compressive residual stresses since it improves fatigue resistance of a material [3, 4]. In the study [5] of the effects of LP parameters such as laser-beam power density, pulse duration, and pulse density it was found that a correct choice of the processing parameters enabled desired variations of micro-hardness and residual stresses in the surface of machine components. Such achieved condition provided improved material resistance to fatigue. The applicability of laser peening was also confirmed to improve stress-corrosion cracking [6]

Laser shock processing as a method of decreasing fatigue of a die-casting die made of maraging steel

Laser Shock Processing (LSP) is a process of laser treatment with a pulsed beam of high-power density. The process generates locally limited mechanical waves that increase the through-depth density of dislocations. This entails a change in mechanical properties, particularly at the workpiece surface. The treatment with laser-induced shock waves is suitable for structural parts and machine elements subjected to high thermo-dynamical loads. LSP can substantially improve the wear resistance, which is of exceptional significance to die-casting tools made of maraging steel. The paper describes the effects of LSP on chosen 12% Ni maraging steel, which is suitable also for the manufacture of tools for die casting of aluminium alloys. After laser treatment, measurements of residual stresses and microhardness and other properties, including surface defects at the micro level, were carried out. The results of the study confirmed that exceptionally favourable residual stresses and microhardness could be obtained

Laser shock peening without absorbent coating (LSPwC) effect on 3D surface topography and mechanical properties of 6082-T651 Al alloy

The influence of nanosecond laser pulses applied by laser shock peening without absorbent coating (LSPwC) with a Q-switched Nd:YAG laser operating at a wavelength of λ = 1064 nm on 6082-T651 Al alloy has been investigated. The first portion of the present study assesses laser shock peening effect at two pulse densities on three-dimensional (3D) surface topography characteristics. In the second part of the study, the peening effect on surface texture orientation and micro-structure modification, i.e. the effect of surface craters due to plasma and shock waves, were investigated in both longitudinal (L) and transverse (T) directions of the laser-beam movement. In the final portion of the study, the changes of mechanical properties were evaluated with a residual stress profile and Vickers micro-hardness through depth variation in the near surface layer, whereas factorial design with a response surface methodology (RSM) was applied. The surface topographic and micro-structural effect of laser shock peening were characterised with optical microscopy, InfiniteFocus® microscopy and scanning electron microscopy (SEM). Residual stress evaluation based on a hole-drilling integral method confirmed higher compression at the near surface layer (33 μm) in the transverse direction (σmin) of laser-beam movement, i.e. − 407 ± 81 MPa and − 346 ± 124 MPa, after 900 and 2500 pulses/cm2, respectively. Moreover, RSM analysis of micro-hardness through depth distribution confirmed an increase at both pulse densities, whereas LSPwC-generated shock waves showed the impact effect of up to 800 μm below the surface. Furthermore, ANOVA results confirmed the insignificant influence of LSPwC treatment direction on micro-hardness distribution indicating essentially homogeneous conditions, in both L and T directions

Effects of laser shock processing on high cycle fatigue crack growth rate and fracture toughness of aluminium alloy 6082-T651

The effects of laser shock processing without protective coating on high-cycle fatigue crack growth and fracture toughness were investigated. Laser shock peening treatment was performed on compact tension specimens from both sides perpendicular to the crack growth direction, followed by subsequent grinding. Fatigue crack growth tests were performed at frequencies between 116 and 146 Hz, at R = 0.1 and a constant stress intensity range during the fatigue crack initiation phase and K-decreasing test. A lower number of cycles was required to initiate a fatigue precrack, and faster fatigue crack growth was found in tensile residual stress field of LSP-treated specimens. The crack growth threshold decreased by 60% after LSP treatment. The fracture toughness decreased by 28-33% after LSP treatment. The fatigue-to-ductile transition boundary on fractographic surfaces show linear fatigue crack fronts in non-treated specimens and curves after LSP treatment