Adriano Scheid

Impact of dilution on the microstructure and properties of Ni-based 625 alloy coatings

Nickel-based alloy IN 625 is used to protect components of aircrafts, power generation and oil refinery due to an association of toughness and high corrosion resistance. These properties are associated with the chemical composition and microstructure of coatings which depend on the processing parameters and the composition of the component being protected. This paper assessed impact of dilution on the microstructure and properties of the Ni alloy IN 625 deposited by Plasma Transferred Arc (PTA) on two substrates: carbon steel API 5L and stainless steel AISI 316L. Differences due to the interaction with the substrate were maximized analyzing single layer coatings, processed with three deposition current: 120, 150 and 180 A. Correlation with a cast Nickel-based alloy sample contributed to assess the impact of dilution on coatings. Dilution was determined by the area ratio and Vickers hardness measured on the transverse section of coatings. Scanning electron and Laser confocal microscopy and X-ray diffraction analysis were carried out to characterize the microstructure. Results indicated the increasing dilution with the deposition current was deeply influenced by the substrate. Dilution ranging from 5 to 29% was measured on coatings processed on the API 5L steel and from 22 to 51% on the low thermal conductivity AISI 316L steel substrate. Differences on the microstructure and properties of coatings can be associated with the interaction with each substrate. Higher fraction of carbides account for the higher coating hardness when processing on API 5L whereas the low thermal conductivity of AISI 316L and the higher Fe content in solid solution contributed to the lower hardness of coatings.

Effect of Track Overlap on the Microstructure and Properties of the CoCrMoSi PTA Coatings

Broadly speaking, the research and design of coatings are generally studied by way of single-track deposits; otherwise, the development of a coated part entails the understanding of how multi-track welding influences the microstructure and properties of the surface. This study evaluated the effect of track overlap on the microstructure and properties of the CoCrMoSi Tribaloy T400 alloy coatings produced on AISI 316L steel substrate. The characterization was performed by scanning electron microscopy, hardness and X-ray diffraction. The correlation between the degree of overlap and performance of the coatings was assessed by wear tests. The single track deposits showed hypoeutectic microstructure as a result of high Iron, Chromium and Nickel content. From the second track on, the chemical composition was displaced back to eutectic and then to hypereutectic with overlap of 25 and 50%, respectively. The microstructure dictated the hardness of the coatings (527 – 701 HV0.5) and the lower mass loss rate was measured for hypereutectic with primary Laves phase.

Analysis of PTA hardfacing with CoCrWC and CoCrMoSi alloys

CoCrWC alloys are widely used to protect components that operate under wear and high temperature environments. Enhanced performance has been achieved with the CoCrMoSi alloys but processing this alloy system is still a challenge due to the presence of the brittle Laves phase, particularly when welding is involved. This work evaluated Plasma Transferred Arc coatings processed with the Co-based alloy CoMoCrSi - Tribaloy T400, reinforced with Laves phase, comparing its weldability to the CoCrWC - Stellite 6, reinforced with carbides. Coatings were also analyzed regarding the response to temperature exposure at 600°C for 7 days and subsequent effect on microstructure and sliding abrasive wear. Coatings characterization was carried out by light and scanning electron microscopy, X-ray diffraction and Vickers hardness. CoCrWC coatings exhibited a Cobalt solid solution dendritic microstructure and a thin interdendritic region with eutectic carbides, while CoCrMoSi deposits exhibit a large lamellar eutectic region of Laves phase and Cobalt solid solution and a small fraction of primary Laves phase. Although phase stability was observed by X-ray diffraction, coarsening of the microstructure occurred for both alloys. CoCrMoSi showed thicker lamellar Laves phase and CoCrWC coarser eutectic carbides. Coatings stability assessed by wear tests revealed that although the wear rate of the as-deposited CoCrMoSi alloy was lower than that of CoCrWC alloy its increase after temperature exposure was more significant, 22% against 15%. Results were discussed regarding the protection of industrial components in particular, bearings in 55AlZn hot dip galvanizing components.

Microstructure and Properties of Nickel-based C276 Alloy Coatings by PTA on AISI 316L and API 5L X70 Steel Substrates

This work assessed Ni-based C276 alloy coatings by PTA with different degree of interaction with AISI 316L and API 5L X70 steel substrates. Track geometry, dilution and microstructure of coatings were evaluated by optical, scanning electron microscopy and X-ray diffraction. Properties were evaluated by hardness and wear tests. Microstructure exhibited austenite Ni-FCC dendrites and interdendrictic regions containing carbides. Dilution from 4,9 to 25,4% for coatings on API 5L X70 leaded to hardness ranging from 283 to 243 HV0,5. Otherwise, dilution between 22,3 and 41,5% for coatings on AISI 316L induced hardness from 267 to 225 HV0,5. Higher interaction with the substrate leaded to 19,8% increase of mass loss rate on API 5L X70 coatings. The slight difference for coatings properties deposited on different substrates indicated that the degree of interaction was the most significant factor.

Effect of processing on microstructure and properties of CoCrMoSi alloy

CoCrMoSi alloys microstructure is affected by processing and their properties have been associated with the high volume fraction of Laves phase. However, not much has been reported on the effect of structure refinement and morphology on the properties of these alloys. This paper evaluates a CoCrMoSi alloy processed by centrifugal casting and Plasma Transferred Arc (PTA) hardfacing, aiming to understand the correlation between microstructure and properties at room temperature in the as-processed condition and following exposure at 600 °C. Characterization was carried out using scanning electron microscopy, X-ray diffraction, hardness and wear tests. The cooling rates associated with each of the processing techniques used account for the developed microstructures and associated hardness, a 626 HV

Influence of Processing on the Microstructure and Properties of CoCrMoSi Alloy PTA Coatings

Wear performance as well as the low toughness of CoCrMoSi alloys is associated with the presence of Laves phase. In light of this, alloying elements have been altered in order to reduce the brittleness of newly-cast alloys. This study evaluated coatings by Plasma Transferred Arc (PTA) with different interactions with the AISI 316L substrate. The higher the dilution, it was hypothesized, the higher Iron, Chromium and Nickel contents proceeding from substrate and, therefore, the lower hard Laves phase fraction. Coatings were characterized by light and scanning electron microscopy, X-ray diffraction and Vickers hardness. Wear behavior was assessed by pin-on-disc and ball-on-flat tests. Laves phase and Cobalt solid solution eutectic lamellar microstructure was observed for coating processed with 120A (18% dilution). The chemical composition was displaced to hypoeutectic, showing Cobalt solid solution dendrites and interdendrictic eutectic lamellar for the coatings processed with higher current intensity (150 / 180A), due to the higher interaction with the substrate (26 / 38% dilution). Dilution increased with the deposition current, causing hardness to decrease from 702 – 526 HV0.5. Wear mass loss rate increased by up to 41.7% and friction coefficient (μ) ranged from 0.45 – 1.06 as the chemical composition changed.

Effect of deposition current on microstructure and properties of CoCrWC alloy PTA coatings

Cobalt-Based alloys are largely applied to the surface of components as welded coatings. Carbides reinforced CoCrWC system is used to extend the service life under harsh environments involving wear and corrosion in different media. This work aims to evaluate the effect of deposition current on the microstructure and properties of PTA coatings. So, CoCrWC alloy (Stellite #6) was processed on AISI316L stainless steel plates with the following main arc current: 100, 120, 150, 180 and 200A. So, different interaction with the substrate must be expected and its effect on coatings features was evaluated. The geometry of single track coatings, dilution, formed phases and phase volume fraction was assessed by laser Confocal, scanning electron microscopy and X-ray diffraction analysis. Vickers hardness and wear tests were carried out to correlate microstructure to properties of coatings. Coatings showed microstructure composed by hypoeutectic dendrites of Cobalt solid solution and interdendrictic carbides. Dilution increased with deposition current from 11,8 e 56,5% which reduced the carbides fraction and increased the Cobalt solid solution areas, resulting in hardness decrease from 500 to 310HV0,5. Higher deposition current induced mass loss rate increase on pin-on-disc sliding wear tests, arising 44,38% increment on wear coefficient, as a consequence of the lower carbides fraction and solid solution alloying and refinement degree of the microstructure.

Elastic Modulus of Oxidized Ti‐Nb Alloys

Titanium (Ti) and Ti alloys are widely used for the manufacture of dental implants and orthopedic prostheses due to suitable properties such as zero toxicity, good mechanical properties and corrosion resistance. The addition of niobium (Nb) to commercially pure Ti (cp-Ti) can results in elastic moduli lower than Ti. So in this work the elastic modulus of Ti-Nb alloys with 10% and 20%, in weight submitted to anodic oxidation (AO) has been investigated to verify how to obtain elastic modulus closer to bone. The AO has been realized using phosphoric acid as electrolyte applying a voltage of 250V/60s. Elastic modulus values were obtained using instrumented indentation technique. The results indicated that it was possible to obtain Ti-Nb alloys with lower elastic modulus values compared with cp-Ti.