Metallurgical Characterization Research Articles

Al2O3-based hybrid composite coatings for mitigating the slurry erosion of an advanced steel in saline and non-saline environments

The present work focuses on the comparative slurry erosion performance evaluation of an advanced steel (ASME SA387) and the alumina-based hybrid coatings for such steels. The study aims to investigate the effect of coatings' properties on their erosion-corrosion behaviour to comprehend their wear performance in saline and non-saline environments. The coatings have been developed by the highly efficient high-velocity oxygen-fuel (HVOF) process. The alumina matrix is reinforced with ceria (CeO2), and hexagonal boron nitride(hBN). A detailed investigation starts with analyzing the coatings' mechanical properties at surface, subsurface and interface regions by using nanoindentation technique, followed by the slurry erosion performance evaluation. To get an in-depth understanding of the materials' performances, various metallurgical characterization techniques like X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and field emission transmission electron microscopy (FESEM) are used. In saline environments, all the materials eroded more when compared to those in non-saline environments. Corrosion-assisted erosion mechanism is found to be the predominant cause of the higher erosion rates in saline slurry medium. Among the coatings, splat detachment and pitting were found to be the erosive wear mechanisms at 30° and 90° slurry flow directions, respectively. However, erosion reduction of ≈ 90 % at 30° impact angle and ≈ 76 % at 90° impact angles were observed for alumina coatings with 0.8 wt% ceria, and 3 wt% hBN additions when compared to the substrate in the saline environments. The observed results were attributed to the metallurgical enhancements in the form of second phases in the coating microstructure, and the mechanical properties at the surface, subsurface, and interface regions.

Comparison between the Effect of Adding MSGNP and B4C-WC Nanoparticles on the Metallurgical and Mechanical Characterization of Al-7075 Composites Produced by Stir Casting

Comparison between the Effect of Adding MSGNP and B4C-WC Nanoparticles on the Metallurgical and Mechanical Characterization of Al-7075 Composites Produced by Stir Casting

Hidden riches in the Early Medieval Rhine Delta: Iron working at Merovingian Oegstgeest

Long dismissed as a backwater, increased study of the Rhine Delta in the Early Middle Ages has revealed considerable wealth and prosperity in even the most isolated of sites. The 6th–8th century Merovingian settlement at Oegstgeest is a good example of such. Despite its seeming remoteness and small size, its excavation found evidence for the creation and importation of quality goods, seemingly without any connection to existing elite structures. This study examined one aspect of this prosperity (iron working) to gain a better understanding of the role of Oegstgeest within its socioeconomic environment. Metallurgical and chemical characterisation was undertaken on thirteen metal samples and twenty-three slag samples from Oegstgeest. The results of this study established the use of quality metals and advanced forging techniques. This suggests that the inhabitants of Oegstgeest had the required contacts to obtain such materials, as well as the presence of skilled artisans with the time and demand to put their experience into practice. Further study found definite evidence of iron and copper alloys being worked in tandem. A provenance study was also undertaken on the metallic samples. Possible matches were established between the material from Oegstgeest with Lorraine in Eastern France as well as a potential connection to Southern Germany. In short, the results of this study suggest complement that of other the other finds of the settlement, suggesting that Oegstgeest was integrated into regional trade networks of the Early Middle Ages.

Root cause analysis of an abnormal groove-clogging failure on sink rolls in continuous hot-dip galvanizing line

In this study, the root cause of an abnormal premature groove-clogging failure on a sink roll in a hot-dip galvanizing line was investigated. Cross-sectional metallurgical characterization was performed on samples obtained from both the groove-clogged and groove-clear sink rolls. Process investigations focused on the Al and Fe concentrations in zinc bath, bath temperature (Tbath), and strip entry temperature (Tstrip). It was found that groove-clogging failure on the sink roll was caused by a large amount of Fe2Al5Znx dross buildup in the grooves, and Tstrip control was the key factor. When Tstrip was consistently lower than Tbath for a long time period during operation, the Fe2Al5Znx intermetallic compounds preferentially precipitated and grew in the locally cooled zinc bath because of the decreased Fe solubility at lower Tbath. When Tstrip was controlled at least 5 ℃ higher than Tbath, the groove-clogging failure was successfully solved.

Wear behavior of bare and coated 18Cr8Ni turbine steel exposed to sediment erosion: A comparative analysis

Hydropower plant components are exposed to sediment erosion due to the impact of hard particles flowing along with the water. As a consequence, significant material loss and substantial reduction in efficiency are encountered during plant operation. This work investigates the sediment erosion problem in hydraulic turbines using a slurry erosion tester. Experiments are performed on bare and coated 18Cr8Ni turbine steel at three impact velocities i.e. 6, 8, and 12 m/s, and two impact angles 30° and 90°. The size of impacting particles varies between 50 to 350 µm with a slurry concentration of 2500 ppm. The erosion rate is found to be maximum at 30° impact angle and minimum at 90° impact angle. With an aim to minimize the erosion of turbine steel, the test samples were coated with in-house formulated ceramic-based coating material using the high-velocity oxygen-fuel thermal spray technique. Vickers hardness test was performed to determine the hardness of the coatings. For metallurgical characterization, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy techniques were used. A comparison of both bare and coated samples is carried out to observe the erosion-resistant aspects. A higher erosion resistance has been detected for the coated material as compared to the bare turbine material. The reduction in the erosion rate for coatings is 13.4% at 30° and 17.62% at 90° impingement angles. The obtained results are related to the tested materials’ microstructural, mechanical, and metallurgical aspects.

Effect of graphene on the tribological behavior of Ti6Al6V2Sn/Gn composite produced via microwave sintering

Titanium alloys are widely used in various industrial applications due to their excellent properties. Due to its excellent heat conductivity and stability, graphene (Gn) can help Ti components last longer and experience less wear. In the current study, Ti6Al6V2Sn (Ti662) with various wt.% Gn was produced. The composite samples were subjected to metallurgical characterization to analyze the influence of Gn addition in the microstructure and phases formed. The properties such as microhardness and wear resistance were analyzed for all the samples. Variations in the load, sliding velocity, and distance were made during the wear test, and the effects of these factors on the wear rate and morphology of the worn surface were examined. Mechanical property analysis revealed that Ti662 + 0.5Gn exhibited the highest microhardness of 514.32HV, which was 1.45 times that of the matrix material. The sample with 0.5Gn exhibited increased wear resistance, the order of wear resistance observed was Ti662 + 0.5Gn > Ti662 + 0.75Gn > Ti662+1Gn > Ti662 + 0.25Gn > Ti662. The wear rate was reduced by 44.15 % at 40 N, 42.07 % and 52.02 % at 1.5 m/s and 2000 m for Ti662 + 0.5Gn composite. Worn surface morphology revealed that at elevated loads, abrasive and delamination wear was observed while at elevated velocity and distance, the formation of mechanically mixed layer (MML) was observed.

Effect of PWHT on metallurgical and mechanical characterization of dissimilar welded joint of P91 and P92 steels

P91 and P92 steels are widely used in nuclear and thermal power plant’s high-temperature (650–700 °C) operating components. The welding procedure, base plate composition, filler material composition, and post-weld heat treatment (PWHT) significantly affect the metallurgical characterization of weldments at room temperature. This work focuses on joining P91 and P92 steel by the TIG welding with filler ER90S-B9. The study analyzes the materialization of coarse-grained HAZ (CGHAZ), inter-critical HAZ (ICHAZ), and fine grained HAZ (FGHAZ) under welded and PWHT. PWHT was conducted at 840 °C for 2, 4 and 6h. An optical microscopic (OM) scanning electron microscope (SEM) was employed to characterize the welded and PWHT samples. It was perceived that the tensile strength of PWHT increased as the heat treatment times increased from 2 to 6 h, while the hardness value decreased accordingly. The maximum tensile strength (594.71 MPa) was observed in PWHT_6 h, while the minimum tensile strength (537.52 MPa) was perceived in the as-welded sample. The PWHT_6h reveals the minimum hardness values (271.12 HV) at the fusion zone among all the conditions. The WFZ consisted of an untampered lath martensitic grain structure, demonstrating an average hardness value of 314.15 HV in the PWHT_2h condition. The hardness value in CGHAZ samples for as-welded, PWHT_2h, PWHT_4h, and PWHT_6h was observed at 456.85, 436.81, 368.63, and 327.41 HV, respectively.

Microstructural analysis of martensitic hard surfacing on low chromium alloy steel

AbstractThis study focuses on the metallurgical characterization of single and multi‐layer martensitic hard surfacing onto non‐standardized low‐chromium alloy steel with a single buttering layer using an automatic submerged arc welding process as a standard reference. The metallurgical properties of hard surfaced samples are examined using an optical microscope, energy dispersive x‐ray spectroscopy, and x‐ray diffractometer. Micro‐Vickers hardness testing is also conducted to analyze and confirm the metallographic results of hard surfacing. The current study finds that the microstructure of each region is influenced by three key factors: chemical composition, heat input, and dilution. The structural type is determined by the chemical composition of materials, heat input influences the structural characteristics in the heat‐affected zone (needle‐shape martensite and tempered martensite), and dilution affects the structural characteristics of the hard surfacing layers (martensite with retained austenite). Comparing multi‐layer hard surfacing to single‐hard surfacing, the hardness values of the heat‐affected zone of the multi‐layer hard surfacing are greatly reduced, while the hardness values of the hard surfacing layers are raised.

Studying the STA effects on aluminium alloy joints by friction welding

This article examines the properties of joints fabricated by friction welding (FW) using AA6061-T6 and AA7075 as examples of both similar and dissimilar metals. It also looks at how heat treatment after welding affects the metallurgical characteristics of the joint. The heat treatment method under investigation combines solutionizing heat treatment with synthetic ageing (STA). The tensile characteristics, microhardness, and microstructure of the as-welded and STA-treated welded specimens are assessed in the paper using mechanical testing equipment and metallurgical characterization methods. The findings demonstrate that the joint characteristics are enhanced by precipitate nucleation occurring in the joint interface of the FW similar and dissimilar joint under STA treatment. On the other hand, the STA influence on the tensile strength (TS) of joints made with AA7075 was greater than that of similar joints made with AA6061-T6, as well as dissimilar joints made with both AA6061-T6 and AA7075. Additionally, after STA treatment, the similar joints showed a uniform distribution of hardness. However, in the dissimilar joint after STA treatment, the hardness dropped suddenly on the AA6061-T6 side, specifically from the partially deformed zone (PDZ) towards the heat affected zone (HAZ).

Mechanical and metallurgical characterization of B4C and SiC reinforced stir casted AA6061 hybrid MMC

The present work was the novel investigation of mechanical and metallurgical characteristics of stir casted AA6061 based metal matrix composites (MMC) and hybrid MMCs. The reinforcements utilized in the investigation were silicon carbide and boron carbide. The thirteen stir casted MMC and hybrid MMC samples were tested for ultimate tensile strength, microhardness, fractography and wear performance. The stir casting process had enhanced the reinforcement distribution within the aluminium matrix. The enhancement in ultimate tensile strength was observed due to the addition of reinforcements in increasing weight percentages with the hybrid MMC exhibiting peak ultimate strength which was a 32.17% improvement against the non-reinforced AA6061 alloy. The formation of reinforcement particulates had enhanced microhardness of the specimens with the peak microhardness observed for boron carbide reinforced MMC exhibiting microhardness 25.41% higher than the base alloy. The hybrid MMC exhibited ductile fracture with highest elongation corresponding to the highest ultimate tensile strength. The wear performance analysis revealed reduced wear rates for the particulate reinforced specimen with highest weight percentage of reinforcements.

Influence of rotational tool speed on metallurgical characterization of friction stir welded joint of AZ91D and AA2024

This study investigated the dissimilar friction stir welding (FSW) of AA2024 and AZ91D and aimed to explore the effect of rotation tool speed (RTS) on welding quality and the formation of intermetallic compounds (IMCs) in the welded region. The optimal welding parameters for achieving a sound weld were determined to be a traverse speed (TS) of 35 mm/min and an RTS of 700 r/min. The presence of two specific intermetallic phases, Al3Mg2 and Al12Mg17, was observed in all joints, with Al12Mg17 showing a tendency to migrate toward the weld surface adjacent to the AZ91D plate, possibly resulting in constitutional liquation during solidification. The results revealed that the morphological characteristics and input heat significantly influenced the formation of IMCs. Moreover, the study highlighted that improper selection of processing parameters, particularly using lower RTS and TS, led to the development of dense layers of IMCs, such as Al12Mg17 and Mg + Al12Mg17, within the stir zone (SZ). Consequently, this led to a decrease in the ultimate tensile strength (UTS) of the FSWed joints. The highest UTS value of 147.26 MPa was achieved with an RTS of 700 r/min and a TS of 35 mm/min, while the lowest UTS value of 113.47 MPa was observed at an RTS of 500 r/min and a TS of 35 mm/min.

Metallurgical Characterization of SS 316L Repurposed by Wire Plus Arc Additive Manufacturing

This research aims to analyze the microstructures and mechanical characteristics of stainless steel (SS) 316L repurposed by wire plus arc additive manufacturing (WAAM). The SS 316L wire is deposited on a SS 316 substrate, which can be repurposed. This deposited material underwent optical microscopy, X-ray diffraction, and tensile test, and the results indicate that it features cellular and columnar dendrites at the bottom and equiaxial grains at the top. The tensile strength of the interface region between the deposited material (DM) and the base material (BM) is the highest (559 ± 4.16 MPa vs. 510 ± 4.93 MPa in DM and 540 ± 2.65 in BM), indicating that the BM and the deposited layers are strongly bonded. All the results from the defect observation, microstructures, and mechanical characteristics confirm the potential of the WAAM process for repurposing.

Investigation of Adding Microscopic Slide Glass Nano Particles on the Metallurgical Characterization and Mechanical Properties of Cast Aluminum 7075 Composites

Investigation of Adding Microscopic Slide Glass Nano Particles on the Metallurgical Characterization and Mechanical Properties of Cast Aluminum 7075 Composites

Effect of welding speeds on the metallurgical and mechanical property characterization of friction stir welding between dissimilar aerospace grade 7050 T7651-2014A T6 aluminium alloys

Friction stir welding (FSW) is an effective technique for producing quality welds and resolving solidification issues of aluminium alloys found in fusion welding (FW) techniques. This study seeks to establish the effect of welding speeds (WSs) of 25, 45, 65, and 85 mm/min with a constant tool rotation speed (TRS) of 1000 rpm and a tool tilt angle (TTA) of 20. Furthermore, mechanical testing was performed to determine the tensile strength, microhardness, and residual stresses. In addition, microstructure characterization was performed using optical microscopy, SEM/EDS and EBSD to identify the quality assurance of the dissimilar AA7050 T7651-AA2014A T6 weld joint. The results indicated that while the WS increased from 25 to 85 mm/min, the width of the stir zone decreased from 9.497 mm to 6.315 mm, according to the macrostructure analysis. Moreover, microstructural analysis reveals the direction of material flow and grain structure on the advancing side (AS) and retreating side (RS) of the thermo-mechanical affected zone (TMAZ) in the weldment. EBSD analysis reveals the 65 mm/min weld joint has a finer grain size (the average grain size is 2 µm) compared to other WS. Residual stress analysis also reveals compressive residual stress in all weld zones except for RS. The RS of residual stress values for 25–85 mm/min weld joints is 3, 7, 4, and 5 MPa. At the same time, UTS values were obtained as 274 MPa (25 mm/min), 317 MPa (45 mm/min), 332 MPa (65 mm/min), and 308 MPa (85 mm/min), and fracture occurred on the RS of all the welded joints, which was confirmed by harness values that are (AS and RS) 115–157 HV and 63–154 HV, respectively. The observed results show that WS at 65 mm/min has better mechanical and metallurgical properties than other welding speeds because of proper material mixing and finer grains obtained in the weldment, which resulted in higher UTS values being attained for WS at 65 mm/min of the FSW joint.

Effect of chemical composition on the electrochemical and wear behavior of boron carbide reinforced copper composites

ABSTRACT. In this work, the Copper composites Cu-x wt. % B4C (x = 0, 5, 10, 15, 20) were fabricated for the metallurgical and mechanical property evaluation as per ASTM standards. The metallurgical characterization tests on the samples include x-ray diffraction, optical microscopy, and scanning electron microscopy with EDX. Further, pin-on-disc apparatus was used to investigate the tribological behavior of composite specimens. An SEM micrograph of the worn surface and wear debris, along with the Gwyddion software, has been used to discuss the wear mechanisms in detail. The Artificial Neural Networks (ANN) classifier model is also constructed to describe the wear behavior in more detail. The experimental results inferred that the addition of Boron carbide particles has enhanced the Copper's corrosion resistance in a 1 M HCl electrolyte solution from 30.34% to 74.2%, 75.08%, and 83.29% with B and C ions. Also, it significantly enhance the mechanical and tribological characteristics considerably.
 
 KEY WORDS: Powder metallurgy, Cu-B4C, Gwyddion, Wear, Artificial Neural Network
 
 Bull. Chem. Soc. Ethiop. 2023, 37(4), 959-972. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i4.12

Exploring friction stir welding for joining 316L steel pipes for industrial applications: Mechanical and metallurgical characterization of the joint and analysis of failure

Efficient welding of pipelines is critical for industries like power plants. Friction stir welding (FSW) has shown the ability to provide higher strength joints and is envisaged to be suitable for joining industrial pipelines as well. Hence, the present study assesses the application of FSW for joining 316L stainless steel industrial grade pipes. The welding is carried out by varying the process parameters, viz., spindle speed (rpm) and welding speed (mm/min), within a suitable range under force control mode. Microhardness and tensile tests have been conducted to evaluate the mechanical strength of the joints, whereas microstructure evaluation by optical microscopy (OM) and field emission scanning electron microscopy (FE-SEM) has been done in order to comprehend the mechanical performance of the weldments. It is found that both the selected welding process parameters (spindle speed and welding speed) have significant influence on the metallurgical and mechanical properties of the welded joints. High grain refinement due to dynamic recrystallization (DRX) in the stir zone results in enhanced hardness. At the optimal combination of parameters, i.e., 400 rpm spindle speed and 50 mm/min welding speed, the weld zone displays higher tensile strength than that of base metal. Also, at the same combination of parameters, stir zone of the welded samples displayed maximum hardness (255HV0.5kg). Some of the weldments displayed early failure during tensile tests. The present study also explains the cause of these failures. Optimum amount of heat generation during FSW process is key to achieving defect free good quality weldments.

Metallurgical characterization and high-temperature tensile failure of Inconel 617 alloy welded by GTAW and SMAW—a comparative study

Two types of the weld joint of Inconel 617 alloy were produced using gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) processes with ERNiCrCoMo-1 filler metal and ENiCrCoMo-1 electrode, respectively. The weld metal showed the segregation of the principle alloying elements like Mo and Cr along the inter-dendritic spaces, triggering the formation of secondary phases. The microstructure characterization of the interface ensured the high dilution, which could be attributed to the closeness in melting point and chemistry of base and filler metal. Microhardness variation, tensile testing at room and high temperature, and Charpy impact test were conducted to investigate the effect of the Mo segregation in the weld zone and heterogeneity in the microstructure of weldments on the mechanical behavior of both the welded joints. The cross-weld tensile tests were conducted at room temperature and 550°C. The tensile test samples failed from the weld zone for each condition with a tensile strength value close to the base metal, which ensured the applicability of the joint for end service. The tensile strength of GTAW-RT, GTAW-HT, SMAW-RT, and SMAW-HT were measured as 766 ± 22 MPa, 570 ± 5 MPa, 760 ± 7 MPa, and 600 ± 8 MPa, respectively. A non-uniform hardness plot was witnessed with the hardness of the GTAW-weld and SMAW-weld zone of 257 ± 8 HV and 285 ± 5 HV, respectively, in the transverse direction. The impact toughness of the weld zone was 84 ± 2 J and 48 ± 4 J for GTAW and SMAW weld zone. The average impact toughness of the GTAW-weld zone was approximately 42% higher than the value of the SMAW-weld zone. In a nutshell, it can be concluded that the welded joint of Inconel 617 produced using the GTAW process with ERNiCrCoMo-1 filler had the best metallurgical and mechanical properties.

Experimental characterization of cyclic behaviour of pure lead: Temperature sensitivity and strain-rate effects

Proton beam pulses with an energy of 20 GeV/c collide with a pure-lead based target installed in the neutron Time-Of-Flight facility (n_TOF) at the European Laboratory for Particle Physics (CERN). The interaction between the proton beam and lead produces neutrons via spallation mechanism and results in a rapid temperature increase and propagation of stress waves. To evaluate the material response in such challenging conditions, a reliable thermo-mechanical characterization is necessary for the calibration of an appropriate constitutive model for pure lead that is valid under cyclic plasticity and high temperature. In this work, the experimental bases for the development of such constitutive material description are lied. Starting with metallurgical characterization, the typical grain size of the material was initially investigated as well as any variations in the metallurgical features. The grains appeared to have an equivalent size ranging from 2 to 6 mm. Then, static tensile tests were conducted at room temperature and different strain-rates from 10−1 to 10−4 s−1. The obtained results were crucial for optimizing the specimen geometry and test setup for the subsequent cyclic tests. Tension-compression cyclic tests were performed at different strain amplitudes from 0.1 to 1.5%, and at three different temperatures (room temperature, 90 °C and 150 °C). The strain amplitudes were controlled by an extensometer and the strain field evolution during the test was recorded by means of 2D DIC.

Non-destructive surface and subsurface characterization of the machined parts by using fiber optic Eddy current sensor

This paper introduces a fiber-optic eddy current sensor (FECS) to enable non-destructive surface and subsurface characterization of the subtractive or additive manufactured metal parts. The surface and subsurface characteristics of the parts are either globally or locally altered by the manufacturing process conditions. Those characteristics can be obtained by nondestructively scanning the machined parts. The proposed FECS consists of a fiber optic sensor for displacement measurement and an eddy current sensor for the subsurface metallurgical property characterization. FECS was designed and devised by winding a copper coil around the probe of the fiber optic sensor. The eddy current is affected by the electrical conductivity and magnetic permeability of the parts. Therefore, the eddy current sensor was used for measuring the magnetic permeability for non-destructive material characterization, and the fiber optic sensor was applied to profile the geometry of the part. The polynomial fitting error of FECS was estimated at 4.77 % for the fiber optic sensor and 0.29 % for the eddy current sensor, respectively. To test the performance of FECS, machined parts under a series of process conditions were fabricated, and those parts were scanned by FECS. As a result, the permeability measured by the FECS showed good agreement with that obtained by a permeability meter for the baseline comparison. Also, the residual stress of those parts measured by X-ray diffraction showed a similar trend to the results obtained by the FECS.

A study on the metallurgical characterisation of the longitudinally sampled friction stir processed TIG welded dissimilar aluminum joints

In this work, one-pass and two-pass friction stir processing (FSP) were applied to the tungsten inert gas (TIG) weldments of AA6082-T651 and AA8011-H14 to analyse the microstructure and tensile characteristics of the weldments. The tests included macrostructure, microstructure, microhardness, tensile testing and fractography. When the one-pass and two-pass FSP were applied to the TIG weldments, the coarse grain structure (grain size 24.63 µm) was transformed into a refined grain structure (grain size 2.632 µm for second pass), thereby eradicating the defects that had been seen before FSP. The tensile strengths of the TIG + FSP passes were more significant than that of the TIG welded joints. The ultimate tensile strength of TIG welding, TIG + FSP 1-pass and TIG + FSP 2-pass were 86.86 MPa, 133.833 MPa and 135.75 MPa, respectively. The tensile strain of the TIG + FSPed joints was found to have a minimal difference from that of the TIG welded joints, with the TIG joint with a higher percentage. The joints’ microhardness post-FSP was more significant than the TIG weldment. The maximum hardness (73.84 HV) at the Nugget zone (NZ) was observed in the TIG + FSP 2-pass welded joint. The results obtained corresponded with the grain sizes of the welded joints; the TIG results displayed a coarse-grained structure, while the TIG + FSP results, regardless of the passes, showed a fine sandwich-arranged grain structure.