Friction Stir Processing Passes Research Articles

Application of friction stir surface treatment for modification of peripheral coarse grain structure and mechanical properties of AZ31 Mg alloy

The presence of peripheral coarse grains (PCG) in the microstructure of extruded products is considered one of the causes of decreased mechanical properties. Such microstructure has been observed at the periphery of extruded AZ31 Mg alloy. This research aims to achieve a refined and homogeneous microstructure at the structure of extruded bars of AZ31 alloy using pinless friction stir processing (FSP). Up to six passes of FSP using pinless tools with different shoulder surface geometries were conducted. Tools with varying diameters of 12, 15, and 22 mm were used to investigate the effect of shoulder geometry. The rotational speed and traverse speed of the tool were set at 900 rpm and 70 mm/min, respectively. The tool tilt angle was also set to 3°. The effect of the tool geometry on the metallurgical and mechanical properties was investigated using metallography tests, microhardness testing, tensile testing, and fracture testing. According to the results, it was found that reducing the diameter of the tool and using featured tool can lead to homogenization and reduction of the average grain size in the processed samples, increasing the microhardness compared to the primary sample. It was also observed that mechanical properties were improved with the increase in the tool diameter due to the improved quality of the processing area. For samples processed with a 22 mm diameter tool, the final strength reached 242.7 and 248.81 MPa, respectively, for the simple and featured tools.

Investigating the Impact of Friction Stir Processing on the Hydrogen Embrittlement in AA6082-T6 Heat-Treatable Aluminum Alloy

AbstractThis study investigates the impact of friction stir processing (FSP) on the hydrogen embrittlement (HE) in AA6082-T6 heat-treatable aluminum alloy. The effects of different number of FSP passes and different hydrogen cathodic charging (HCC) conditions on the material’s response to HE are examined through comprehensive mechanical testing, microhardness analysis, and microstructural characterization. The results revealed that FSP leads to a decrease in yield strength, ultimate tensile strength, and microhardness, accompanied by an increase in energy absorption. The introduction of hydrogen through HCC significantly reduces mechanical properties, particularly in non-FSPed specimens. Notably, specimens with 8 FSP passes exhibit an interesting behavior with a slight increase in energy absorption and microhardness values after HCC. Microstructural analysis shows that FSP refines the microstructure, resulting in enhanced resistance to hydrogen-induced blistering effects. These findings contribute to the understanding of hydrogen embrittlement in FSPed aluminum alloys, providing insights for developing surface-modified materials suited for hydrogen-rich applications. Graphical Abstract

Analyzing the Influence of Microstructure on the Mechanical Properties of TIG Welded Joints processed by Friction Stir considering the sampling Orientation

The contribution of the microstructural arrangement to the mechanical properties of friction stir processed Tungsten Inert Gas (TIG) welded joints is reported in this work. The TIG-welded joints were subjected to a single pass of Friction Stir Processing (FSP). The friction stir processed joint was sampled transversally and longitudinally, and different tests were conducted and studied comparatively. The microstructural analysis showed refined grains with varying degrees. The mean grain size for the transversally sampled specimen was found to be 11.48 µm, while the longitudinally sampled specimen had varying mean grain size from 7.32 µm to 15.09 µm. The varying mean grain size of the longitudinally sampled specimen is caused by the staggered arrangement of the microstructure. The tensile properties and the microhardness of the transversally sampled specimen were lower than those of the longitudinally sampled specimen. The ultimate tensile strength of the transversally sampled specimen was found to be 87.88 MPa which is lower than that of the longitudinally sampled specimen (133.83 MPa). The microhardness of the longitudinally sampled specimen fluctuated between 30 HV and 80 HV while the transversally sampled specimen had a maximum microhardness of approximately 57 HV.

Effect of multiple passes on the properties of Al-5052/SiC surface composites fabricated via friction stir processing

Friction stir processing (FSP) has emerged as a promising technique for producing surface composites with enhanced mechanical, microstructural and tribological properties. This work investigates the influence of multi-pass FSP on various properties of aluminium 5052 alloy reinforced with silicon carbide (Al-5052/SiC). The results indicated that multi-pass FSP effectively dispersed SiC particles within the aluminium matrix, resulting in a refined microstructure and improved mechanical properties. As the number of FSP passes increased, hardness, tensile strength, and wear resistance improved, reaching levels significantly higher than the base Al-5052 alloy. Tensile strength, yield strength, and average microhardness in the five-pass FSPed specimen were improved by about 25 %, 26 %, and 28 % respectively. Wear and corrosion resistance improved with the increase of FSP passes. The quantitative results of the study strongly corroborate with microstructural evolution.

Enhanced strength ductility and wear resistance in a friction stir processing engineered AZ31B/TiC magnesium-based nanocomposites

ABSTRACTIn the present investigation, efforts have been made to fabricate a magnesium-based AZ31B nanocomposite by integrating nano-sized titanium carbide (TiC) particles via utilising the friction stir processing (FSP) process. The primary objective of the research was to enhance the metallurgical, mechanical, and tribological properties of the base material while investigating the influence of secondary phase particles and various FSP parameters. The findings were rigorously validated through a comprehensive analysis, which encompassed the use of various testing apparatus, such as optical microscopy, field emission scanning microscopy, microhardness testers, tensile and compressive testing machines, along with fractography analysis for wear morphology and tensile properties. The results indicate that the nanocomposite produced under the conditions of a tool rotation speed of 1600 rpm and a transverse speed of 40 mm/min along with three number of FSP passes exhibits superior mechanical and tribological properties compared to both other developed composites and the base alloy. A significant enhancement of nearly 2.68 times in microhardness values along with simultaneous refinement in grain size up to 14.85 times was obtained. Ultimate tensile and compressive strengths report an impressive increase in values up to 2.16 and 1.6 times respectively when compared to the base metal. Furthermore, the tensile fracture behaviour of the base magnesium alloy indicated brittleness, while the AZ31B/TiC composite displayed a combination of ductile and brittle features. In terms of wear morphology, the base magnesium alloy exhibited adhesive and abrasive wear, while the composite demonstrated particle pull-out, delamination, and localised plastic deformation, with enhanced resistance to wear. These findings underscore the significant improvements achieved in mechanical and tribological properties, thus emphasising the novel contributions of this research to the field.

Effects of friction stir processing and nano-hydroxyapatite on the microstructure, hardness, degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications

Nowadays, magnesium alloys are emerging in biomedical implants for their similar properties to natural bones. However, the rapid degradation of magnesium alloys in biological media hinders successful implantation. Refinement of microstructure, as well as reinforcement particles can significantly improve the degradation rate. In this work, multi-pass friction stir processing (FSP) was proposed to synthesize WE43/nano-hydroxyapatite (nHA) surface composite, the microstructure, reinforced particle distribution, micro-hardness, corrosion behavior and in-vitro bioactivity were studied. The subsequent FSP passes of WE43 alloy and WE43/nHA composite refined the grain size which was reduced by 94.29% and 95.92% (2.63 and 1.88 µm, respectively) compared to base metal after three passes. This resulted in increasing the microhardness by 120% (90.86 HV0.1) and 135% (105.59 HV0.1) for the WE43 and WE43-nHA, respectively. It is found that increasing FSP passes improved the uniform distribution of nHA particles within the composite matrix which led to improved corrosion resistance and less degradation rate. The corrosion rate of the FSPed WE43/nHA composite after three passes was reduced by 38.2% (4.13 mm/year) and the degradation rate was reduced by 69.7% (2.87 mm/y). This is attributed to secondary phase (Mg24Y5 and Mg41Nd5) particle fragmentation and redistribution, as well as a homogeneous distribution of nHA. Additionally, the growing Ca-P and Mg(OH)2 layer formed on the surface represented a protective layer that reduced the degradation rate. The wettability test revealed a relatively hydrophilic surface with water contact angle of 49.1 ± 2.2° compared to 71.2 ± 2.1° for base metal. Also, biomineralization test showed that apatite layer grew after immersion 7d in simulated body fluid with atomic ratio of Ca/P 1.60 approaching the stoichiometric ratio (1.67) indicating superior bioactivity of FSPed WE43/nHA composite after three passes. These results raise that the grain refinement by FSP and introduction of nHA particles significantly improved the degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications.

Optimization of friction stir processing parameters for improving structural and mechanical properties in in situ AA5083-H111/Al–Fe composites

The primary focus of this study is the application of friction stir processing to produce surface composites of in situ AA5083-H111/Al–Fe. These composites were fabricated by mixing mechanically alloyed Fe–40 wt% Al powder for 40 h. The AA5083 substrate underwent a two-pass friction stir processing with changes in the tool’s movement direction during fabrication. This experiment used Taguchi’s L9 orthogonal array design to gather and analyse data efficiently. Following each friction stir processing pass, the fabricated aluminium metal matrix composite microstructure, hardness and ultimate tensile strength were conducted. In this study, the maximum tensile strength of 225.8 MPa after the first pass and 253.6 MPa after the second pass. Additionally, microhardness measurements indicated values of 123.3 and 128.3 Hv after the first and second passes, respectively. These impressive mechanical properties were achieved by optimizing specific process parameters, including a tool shoulder diameter of 21 mm, a tool rotational speed of 900 rpm, a tool traverse speed of 63 mm/min and a tilt angle of 1.5°. Furthermore, examining the fracture surface of the friction stir processed sample revealed ductile failure behaviour, suggesting that the material experienced deformation and stretching before fracture. This observation aligns with the inherent ductile nature of the AA5083/Al–Fe composite.

Friction stir processing of AZ31 alloy to improve the mechanical, biodegradation, and in vitro biocompatible characteristics

The aim of the study was to improve the mechanical, biodegradation and in vitro biocompatible characteristics of as received rolled AZ31 (Mg-1%Zn-3%Al) alloy by develop the surface composite of Mg-Titania. The surface composite was developed by friction stir processing (FSP) and it’s used for prosthetic applications. The influence of tool rotation speed and number of FSP passes on grain structure, grain refinement, tensile strength, hardness, in vitro degradation rate and in vitro biocompatibility were explored. The obtained results support the capability of FSP in terms of mechanical strengthening, refinement of grain structure, dispersion of reinforcement (i.e. TiO2) and controlled degradation rate. Grain structure at stir zone, advancing side and retreating side were investigated. The large grains in the alloy were reduced to a fine equiaxial grains of average dimension of 3 μm by 3rd pass of FSP. The process was performed under two different tool rotation speed, i.e. 1550 and 2260 RPM. The addition of second phase in the matrix significantly improve the grain refinement. The results obtained from tensile test revealed the improvement in the percentage elongation without compromising the strength. The micro hardness of specimens of different parametric combination were evaluated and found 30–50% improvement in the micro hardness. The degradation rate by immersion test in simulated body fluid (SBF) for 3, 6 and 10 days were performed and found a significant reduction in degradation rate. The MTT assay for the biocompatibility performed by indirect method, the results validate the non-toxic behavior of processed specimen.

Influence of tool plunge depth and multiple passes on the microstructure, texture evolution and hardness of age-hardenable aluminium 7075 alloy

In this study, the surface properties of AA7075 were modified through the solid-state friction stir processing technique using a hexagonal-shaped H13 pin. Single pass friction stir processing was conducted at two different shoulder plunge depths at constant tool rotation and linear speeds with the resulting cross-sections being examined using optical macroscopy. Six friction stir processing passes were then carried out intermittently at optimal shoulder plunge depth and the corresponding microstructural evolution along the nugget was investigated using advanced microstructural characterization techniques such as electron backscatter diffraction and high-resolution transmission electron microscopy. Bulk texture examination was conducted using the neutron diffraction method, while hardness measurements were taken using Vicker's hardness testing machine. Single pass friction stir processing conducted at a shoulder plunge depth of 0.25 mm produced defect-free material consolidation with a refined grain structure along the nugget. Minimum grain size averaging 3.78 μm was observed at the top, while slightly increased grain sizes were noticed at the middle and bottom regions of the nugget. After 6 friction stir processing passes, grain size was reduced significantly averaging 1.84 μm at the top, while size at the pin-driven zone exhibited an increasing trend due to heat input and strain rate variations. Both, single-pass and 6 pass specimens exhibited a weaker texture along the nugget due to randomness in grain orientation and the effect of particle-stimulated nucleation mechanism. In the single-pass specimen, hardness decreased along the nugget, with a maximum of 85.2 HV at the top, while 6-pass specimen exhibited an improved hardness of 133.5 HV due to the strengthening caused by grain refinement, precipitates and dislocations.

Effect of reinforcement particles and multipass of friction stir processing on microstructure and mechanical properties of aluminium alloy

The present study focuses on the successful fabrication of aluminium metal matrix composites (AMMCs) using friction stir processing (FSP) and micro-sized SiC as reinforcement particles (RPs). The microstructure of Al6061-T6/SiC AMMCs in the stir zone was examined using Electron Backscatter Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). The incorporation of SiC particles and the refinement of grain structure resulted in upgraded mechanical properties of the AMMCs achieved through three FSP passes. These enhancements were concerning from the reduction in grain size and more orderly dispersal of SiC particles. Moreover, the microhardness of the AMMCs enhanced by 41.79%, by augmenting the FSP passes, which can be characterized by the refinement in grain structure, facilitated by the dynamic recrystallization (DRx) mechanism.

Fabrication of Al matrix composite reinforced with Fe-Cu particles using friction stir processing

Friction stir processing (FSP), as an advanced technique, was employed to fabricate in situ aluminum composites with the aim to elucidate the correlation between microstructure and mechanical properties of the obtained composites. The novelty of the work is to utilize simultaneous incorporation of Fe and Cu powders into the friction stir zone in order to fabricate in situ aluminum composites. To achieve the goal, the loading content of Cu and Fe powders and the process pass number (1 pass to 5 passes) were altered. While the total loading content of Fe and Cu powders was kept constant, the weight percentages of these reinforcements were varied (25%, 50%, and 75%). Microstructural characteristics were examined using scanning electron microscopy and optical microscopy. Five passes FSP resulted in smaller grain sizes of the Al matrix, smaller and less agglomeration of the reinforcements as well as homogeneous dispersion of the reinforcement features and thus, enhancement of the mechanical properties of the composites. X-ray analysis and energy dispersive spectroscopy confirmed in situ formation of Fe-Al and Al-Cu intermetallic compounds in the composites. The tensile testing outcomes proposed the 50wt% Fe-50wt% Cu/Al composite fabricated in 5 passes as the optimum formulation achieved in this research. This can be attributed to the smaller grain size of the matrix in the friction stirred zone and more homogeneous dispersion of the reinforcements in the matrix. Furthermore, this strengthening was affected from the presence of more amounts of well dispersed intermetallic compounds in situ formed during 5 passes. The average tensile strength (207 MPa) and hardness (73 Vickers) of the composite were approximately 175% and 160% greater than that of the unreinforced aluminum (75 MPa, 28 Vickers), respectively. Increasing the process pass number from 3 to 5 passes not only had strengthening and hardening effects but also improved the composite elongation at break.

Microstructure and mechanical properties of tungsten inert gas welded dissimilar aluminum alloys joint subjected to normal multi-pass friction stir process

This work investigated the effect of multi-pass friction stir processing on the tungsten inert gas welded joints of AA6082/AA8011. The friction stir processing approach is broadly used in the marine, automotive, and aerospace engineering sectors. The flow of plasticized material seems to be significant in the mixed flow region, which causes an erratic intercalation pattern. By using a stirring tool action, deformation was induced in situ extrusions of dissimilar alloys. The plasticized material was moved layer by layer to generate a lamellae structure. Theparent materials AA6082 and AA8011 were seen to be penetrating and vigorously mixing in this zone. After the fourth pass friction stir processing, the tungsten inert gas weldment's ultimate tensile strength and % strain dramatically increased. The defects that had been present before friction stir processing were eliminated when the coarse grain structure of the tungsten inert gas weldments was changed into a refined grain structure from 18.09 to 8.92 µm. The microstructure study shows the linear relationship between friction stir processing passes and grain size. The increases in friction stir processing pass resulted in a decrease in grain size. The maximum ultimate tensile strength (89.60) was observed in tungsten inert gas + 4 pass friction stir processing compared to the other joints.

Influence of pass number on microstructure, mechanical, and tribological properties of cold-rolled Al1050 during friction stir processing

In this investigation, cold-rolled Al1050 sheets underwent various passes of Friction Stir Processing (FSP), namely one, three, and five. Then, microstructural evolution was assessed by focusing on underlying restoration phenomena, including severe dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX), and their corresponding effects on mechanical and surface properties were evaluated. Findings illustrated that initial cold-rolling on Al1050 and its high stacking fault energy are the primary driving forces for accelerating DRV, contributing to the supremacy of the DRV-induced softening over sub-grain strengthening caused by CDRX. Increasing the FSP pass number resulted in a drop in yield stress (YS), ultimate tensile strength (UTS), and microhardness values of the FSP-treated samples such that the UTS of one, three, and five passes FSPed samples decreased by ∼18 %, 32 %, and 35 %, respectively, compared to the cold-rolled Al1050. Conversely, the %elongation of the FSP-treated samples dramatically increased with increasing FSP pass number, which is evident from stress-strain curves and the fracture surfaces. Furthermore, increasing the FSP pass number increased the mean coefficient of friction (MCOF) and weight loss during the pin-on-disk test. Also, conducting various passes of FSP improved corrosion resistance compared to the base metal. However, increasing the FSP pass number reduced the corrosion resistance due to grain growth such that the one-pass FSPed sample illustrated better corrosion resistance than the five passes FSPed sample. Repeating the FSP led to excessive frictional heat input to the matrix, contributing to grain growth after increasing FSP passes, thereby decreasing mechanical properties and corrosion resistance.

Evolution of microstructure and strength of a high entropy alloy undergoing the strain-induced martensitic transformation

In a recent work, we have reported outstanding strength and work hardening exhibited by a metastable high entropy alloy (HEA), Fe42Mn28Co10Cr15Si5 (in at. %), undergoing the strain-induced martensitic transformation from metastable gamma austenite (γ) to stable epsilon martensite (ε). However, the alloy exhibited poor ductility, which was attributed to the presence of the brittle sigma (σ) phase in its microstructure. The present work reports the evolution of microstructure, strength, and ductility of a similar HEA, Fe38.5Mn20Co20Cr15Si5Cu1.5 (in at. %), designed to suppress the formation of σ phase. A cast and then rolled plate of the alloy was processed into four conditions by annealing for 10 and 30 min at 1100 °C and by friction stir processing (FSP) at tool rotation rates of 150 and 400 revolutions per minute (RPM) to facilitate detailed examinations of variable initial grain structures. Neutron diffraction and electron microscopy were employed to characterize the microstructure and texture evolution. The initial materials had variable grain size but nearly 100% γ structure. Diffusionless strain induced γ→ε phase transformation took place under compression with higher rate initially and slower rate at the later stages of deformation, independent on the initial grain size. The transformation facilitated part of plastic strain accommodation and rapid strain hardening owing to a transformation-induced dynamic Hall-Petch-type barrier effect, increase in dislocation density, and texture. The peak strength of nearly 2 GPa was achieved under compression using the structure created by double pass FSP (150 RPM followed by 150 RPM). Remarkably, the tensile elongation exhibited by the alloy was nearly 20% with fracture surfaces featuring a combination of ductile dimples and cleavage.

Assessment of microstructure, biocompatibility and in-vitro biodegradation of a biomedical Mg-Hydroxyapatite composite for bone tissue engineering

In the present study, an Mg-based biomedical composite is fabricated by addition of Hydroxyapatite bioactive nanoparticles into a substrate of bioabsorbable WE43 Mg alloy using multi pass friction stir processing (FSP). The findings indicate that applying 6 passes of FSP leads to a decrease of grain size by over 93%, crushing and redistribution of secondary phase particles within the Mg matrix, improved homogeneity of Hydroxyapatite bioactive particles and a reduction in their agglomeration. In vitro Biodegradation tests prove that as the number of FSP passes increases, the weight loss of fabricated bio-composites and biodegradation rate in simulated body fluid (SBF) decrease. Bioactivity of Mg-based bio-composites is assessed by in vitro immersion in SBF for 28 days. Biomineralization process shows that all fabricated Mg-Hydroxyapatite bio-composites exhibit bone-like apatite forming ability, and cauliflower-shaped Hydroxyapatite crystals form on their surface. Moreover, increasing the uniformity of Hydroxyapatite particles stimulates formation of cauliflower-shaped Hydroxyapatite denser crystals, which improves biocompatibility of bio-composites. Biocompatibility of fabricated bio-composites is also evaluated by MTT assay and DAPI staining. Mg-HA-6P demonstrates the highest number of healthy flattened spindle shaped L-929 fibroblast cells with 83.36% cell viability after 5 days of incubation compared to other samples. Increasing number of FSP passes causes high bioactivity, low biodegradation rate and homogeneous distribution of Hydroxyapatite particles, which in turn improve the viability of L-929 fibroblast cells. Furthermore, with the addition of Hydroxyapatite particles and an increase in the number of FSP passes, the yield strength values of the samples increase, reaching 212 MPa and 226 MPa for the Mg–6P and Mg–6P-HA samples, respectively.

An overview of friction stir processing of Cu–SiC composites: Microstructural, mechanical, tribological, and electrical properties

Copper matrix composite reinforced with SiC exhibits high electrical and thermal conductivity, as well as superior mechanical properties, making it a potential candidate for thermal management applications. There has been rapid progress in the understanding of Cu–SiC metal matrix composites during the past decade. To accomplish this, powder metallurgy, casting, selective laser melting, composite electroforming technology, and electrodeposition methods have been employed. The optimum cutting conditions for fabrication of Cu–SiC metal matrix composites are still being explored. In recent years, friction stir processing (FSP) has become increasingly popular in the fabrication of composites. FSP is capable of microstructural engineering in Cu–SiC systems. In light of the fact that the electrical/thermal conductivity and mechanical performance of Cu–SiC composites depend on microstructural characteristics such as SiC distribution, grain size, grain orientation, density of dislocations, and bulk density, it seems important to study the effect of manufacturing conditions on microstructure in detail. In this study, the influence of FSP parameters such as rotational and traversal speeds, the number of FSP passes, and the pin profile as well as the characteristics of SiC powder are discussed in detail with regard to macro- and microstructure, hardness, strength, tribological, and electrical properties of FSPed Cu–SiC composites.

Effect of multipass friction stir processing on microstructure and mechanical properties of MIG welded joints of AA6082 and AA7075

Metal inert gas (MIG) welding is widely employed for aluminum alloy welding, but high residual stress, coarse grain’s structure, porosity, and micro-cracks occur during MIG welding. To avoid these defects, friction stir processing (FSP) was employed to the MIG welded joints of AA7075 and AA6082 with ER4043 filler. The grain structure of the weld fusion zone (WFZ) was categorized by eutectic precipitated Mg2Si, and primary α-Al. The elongated, coarse grain structure of the MIG weldment decreased after a one pass FSP. The Mg2Si precipitates were disseminated due to the enhancement of dispersion and dissimilar metal fraternization. The fraction area of the refined grains increases when the FSP pass increases. Furthermore, the effective enhancement of the joint efficiency was observed in the MIG + 4Pass FSP due to the grain refinement. The ultimate tensile strength (UTS) of 169.73 MPa of the MIG welded joint was observed with a grain size of 17.9 ± 0.3, while the highest UTS of 223.84 MPa was perceived at 4 passes of MIG + FSP joints with an elongation of 12.45%. The grain structure was also refined as the FSP pass increased, and the minimum grain size (2.6 ± 0.3 µm) was perceived at MIG + 4Pass FSP. Multipass FSP leads to refinement and homogenization of the microstructure, increasing the microhardness of the weldment. The average hardness value of the MIG weldments at the WFZ was 84 HV, while the microhardness of MIG + FSP joints of 1Pass, 2Pass, 3Pass, and 4Pass FSP was 88, 96, 101, and 110 HV at the stir zone (SZ).

Rapid grain refinement and compositional homogenization in a cast binary Cu50Ni alloy achieved by friction stir processing

Friction stir processing (FSP) has been increasingly adopted for joining and processing materials in automotive, aerospace and industrial construction. During FSP a dynamic competition between high-speed shear deformation and deformation-induced heating brings about a complex competition between multiple dynamic microstructural evolution mechanisms making it difficult to predict the microstructural evolution pathway. Hence, improved understanding of microstructural evolution mechanisms during FSP can be beneficial for continued growth in the adoption of FSP for demanding applications of future. Towards this goal, this study uses a model binary Cu – 50 at.% Ni alloy to clarify the effect of single and double pass FSP on the microstructural evolution of a coarse grained and compositionally heterogeneous cast microstructure. High energy synchrotron X-ray diffraction, electron backscatter diffraction, and nanoindentation are used to clarify the microstructural evolution due to FSP. The process of compositional homogenization of as-cast segregations is studied by energy dispersive spectroscopy and atom probe tomography. Our results show that a single fast FSP pass at 30 mm.s−1 produces a 100 μm deep layer of submicrometric and hall-petch hardened CuNi grains. The initial cast compositional heterogeneities in a micrometric scale is rapidly transformed to nano-sized domains, mainly confined at grain boundaries. Double pass FSP increases the penetration depth of the processed layer and leads to a 2.9 times grain growth relative to single pass FSP. Grain fragmentation, discontinuous dynamic recrystallization, grain growth, and twinning mechanisms are discussed. These results highlight the value of FSP for ultrafast grain refinement and compositional homogenization of cast alloys.

Fabrication of osteogenesis induced WE43 Mg-Hydroxyapatite composites with low biodegradability and increased biocompatibility for orthopedic implant applications

Good biocompatibility, low biodegradation rate and excellent mechanical properties are essential for desirable performance of metallic biomaterials during osseointegration process. In the present study, bioabsorbable WE43 Mg alloy was used for fabrication of bio-composites with addition of nanosized hydroxyapatite (HA) particles by means of multi pass friction stir processing (FSP) for orthopedic implant applications. Microstructure, in vitro biodegradation and biocompatibility, wettability, and microhardness of resultant bio-composites were characterized. Results showed that applying severe plastic deformation through FSP caused significant grain refinement of Mg matrix and homogenous dispersion of fragmented secondary phase particles. Moreover, applying higher number of FSP passes increased uniformity of distribution of HA nanoparticles throughout Mg matrix. Compared to coarse grain samples, grain refined samples showed lower Mg2+ concentration and H2 evolution in simulated body fluid (SBF). Moreover, addition of HA into Mg matrix, reduced Mg2+ release and H2 evolution. The bio-composites illustrated uniformly and flatly corroded surface compared to samples without HA nanoparticles. During immersion of the bio-composites in SBF solution, a cauliflower structure of Ca–P compounds deposited on the surface of bio-composites which confirmed acceptable biomineralization. Contact angle measurement demonstrated that wettability of fabricated bio-composites increased by increasing number of FSP passes. Mouse osteoblast MC3T3 cell culture indicated that the fabricated bio-composites with uniform distribution of HA nanoparticles showed excellent in vitro biocompatibility, cell viability, and cell proliferation. Eventually, it was found that applying further FSP and presence of HA nanoparticles resulted in increased microhardness which is an indication of higher load-bearing capability of the fabricated bone implants.

Corrosion behavior and tribological-microstructural characterization of Al/ZrO2-Gr hybrid composite fabricated via Friction Stir Processing

The present study investigates the microstructural evolution, tribological properties, and corrosion behavior of hybrid metal matrix composites reinforced by a combination of graphite (Gr) and zirconia (ZrO2) particles fabricated by Friction Stir Processing (FSP). To do so, microstructural characterization was carried out by optical microscopy (OM) and electron backscatter diffraction (EBSD) analysis. In addition, pin-on-disk, microhardness measurement, potentiodynamic polarization, and electrochemical impedance tests were conducted to evaluate the tribological and corrosion behavior of the samples. Results showed that employing four passes of FSP led to significant grain refinement in stir zones because of dynamic recrystallization (DRX), particle-stimulated nucleation (PSN), and Zener pinning effect. Furthermore, the EBSD results illustrated that the average grain size area has significantly decreased from ∼115 µm2 in the only FSP-treated specimen to ∼1.2 µm2 in the hybrid composite. Also, the presence of the secondary phase particles caused an increase in the fraction of the high-angle grain boundaries (HAGBs) compared to the only FSP-treated specimen. The results of the pin-on-disk test revealed that the wear resistance improved in the particle-reinforced composites and, on the other hand, decreased in the FSP-treated sample compared to the base metal (BM). Furthermore, the lubricant effect of the Gr particles contributed to a pronounced reduction in the coefficient of friction (COF) and weight loss in the Gr-containing composites such that the COF of the hybrid composite and Gr-reinforced mono-composite dramatically decreased by ∼0.52 and ∼0.37, respectively. The corrosion behavior of the FSP-treated sample demonstrated better resistance compared to the BM. In addition, the particle-reinforced composites exhibited better corrosion resistance than the FSP-treated sample and BM, especially the Al/Gr mono-composite which had the minimum corrosion rate and the most positive pitting potential (Epit), making it the most pitting-resistant sample in comparison to other specimens.