Similar Alloys Research Articles

Corrosion studies, parameter effects, and surface morphology of AA5052-AA6101T6 friction stir welded joints

Traditional fusion welding is unsuitable for welding aluminum alloys because secondary brittle phases, porosity, and cracks are likely to form as the alloy solidifies. Friction stir welding (FRSTW), a new solid-state welding method, can join similar or dissimilar aluminium (ALU) alloys. In this study Friction stir welded AA5052-AA6101T6 alloy samples were tested for corrosion characteristics. The microstructure and mechanical behavior of FRSW-welded AA5052-AA6101T6 ALU alloy joints were examined relative to input parameters. Microstructure reveals that welding speed and rotation-speed affect the weld microstructure analyzed sample welded areas. Twenty-nine samples were corrosion tested in 3.5% NaCl, household water (880 ppm - SPM), 1N H2SO4, 1N NaOH, and natural seawater for 72 hours. Domestic salt water and acid medium showed better resistance to corrosion than alkaline and salt media. Impedance studies demonstrated slight anodic and cathodic potential changes after friction stir welding.

STRENGTHENING OF THE CARBIDE ALLOY OF WOOD CUTTING SAWS WITH COMPOSITE MATERIALS

The article covers issues related to the strengthening of solid tungsten-cobalt alloy plates of wood-cutting disc saws with new tungsten-free composite materials. It is shown that the domestic hard alloy is significantly inferior to the similar hard alloy of foreign production. This is primarily related to the technology of its production (the imperfection of the equipment for grinding tungsten, which does not make it possible to obtain the required dispersion and the method of sintering). It is noted that one of the ways to solve these problems is the development of a technology for strengthening hard alloy plates, which will make it possible to increase the stability indicators of the tool. Wear resistance can be increased by special surface treatment with the help of new composite materials, which changes such properties of the main material as hardness, corrosion and operational wear resistance, and strength. The problem of surface strengthening of wood-cutting tools with the use of wear-resistant coatings is quite urgent, as it opens wide opportunities for the creation of new special materials with fundamentally new physico-mechanical and physico-chemical properties. Advanced technologies for obtaining such coatings include the method of their formation under the action of concentrated energy flows with the use of electrospark alloying. The main advantage of the surface treatment of materials is that despite the high hardness and strength of the surface layer, the high plasticity and viscosity of the base is preserved. That is why research aimed at strengthening wood-cutting saws with new materials using the electrospark alloying method is relevant. The purpose of the research is to increase the service life of the wood-cutting tool by electrospark alloying of hard alloy with new composite materials and to reduce the shortage of hard alloys. The research results showed that dusts with strengthening treatment of teeth with a material based on titanium carbide КТФХ have the greatest resistance.

Impact of Friction Stir Spot Welding Process Parameters on Weld Strength for Similar Aluminum Alloys

Impact of Friction Stir Spot Welding Process Parameters on Weld Strength for Similar Aluminum Alloys

A Review of Friction Welding Research Addressing the Influence, Development, Similar & Dissimilar Welding

This review paper discusses the recent research work carried out in the frictional joining of dissimilar and similar alloys through the friction welding (FW) process with various parameters and modifications. It includes further the latest developments and advances in the research on FW and the influences of FW’s process parameters on the quality of joints and their properties. The specimens’ faying surfaces can also influence the joint properties as the surface modifications stimulate or change the metal joints’ bonding according to the welding parameters selected during FW. Though the rise of friction pressure (FP) during FW improves the strength of the joints, the improper selection of parameters leads to metal damage. It feels better if the axial shortening is less than 30 mm for FW of soft metals. The axial shortening values are less than 25 mm for the hemispherical bowl-type faying surfaces under 18 bar FP and it is noted that the bevel-type tapered faying surfaces increase the shortening. FW provided very narrow weld interfaces with around 5-10 µm width. With a low FP, it was possible to obtain a maximum of 100 % efficiency by modifying their faying surfaces. The small-diameter soft material needs less FP and friction time. The microstructure modification is possible and the weld joint is shown as U and V shapes for the bowl and tapered faying surfaces. It further increases the contact area and thus increases strength.

Material characterisation of anodising effects on small fatigue crack nucleation in AA7XXX alloys

The precursor cleaning steps in the anodising surface finish process for aluminium alloy aircraft parts are known to lead to etching of surface-breaking intermetallic particles and grain boundaries, which in turn leads to preferential sites for fatigue crack nucleation. Type 1C anodising per MIL-A-8625F, is a favoured aircraft aluminium part corrosion protection treatment meeting modern health and environmental requirements. Type 1C anodising uses electrolysis in a non-chromic acid bath (typically based on sulphuric, boric-sulphuric or phosphoric acid formulations) to develop a thick aluminium oxide surface layer. In previous studies the equivalent initial damage sizes of these nucleation sites was calculated from near surface fatigue crack growth measurements using quantitative fractography in both Type 1C anodised aluminium alloy 7050-T7451 and 7085-T7452. A notable difference was observed in the values for these two materials with AA7085-T7452 equivalent initial damage sizes being significantly smaller. Since these values are critical crack starting size assumptions in fatigue life analysis for aircraft fleets, the observed differences must be investigated and explained for notionally similar alloys under identical conditions.In this work, the material surrounding the population of crack nucleation sites in several Type 1C anodised fatigue tested specimens manufactured from AA7050-T7451 and AA7085-T7452 materials has been characterised using precise surface preparation methods and scanning electron microscopy techniques. It has been demonstrated that there is a statistically significant difference in the number, size, aspect ratio and distribution of surface breaking Al7Cu2Fe intermetallic particles beneath the anodising layer that, when etched out during the anodising process, are responsible for fatigue crack nucleation in 7050-T7451 over 7085-T7452 material. The increased size, angular shape and coverage of these intermetallics in AA7050 serves to increase their effectiveness as preferential locations for fatigue crack nucleation through two mechanisms, as a highly localised stress concentrating feature, as well as through their ability to sample more of the material's microstructural features ensuring a discontinuity is present in the most favourable orientation and location for fatigue crack nucleation.

Recurrent neural network based on attention mechanism in prediction of glass forming ability by element proportion

The traditional trial and error method is time-consuming and laborious to study glass forming ability (GFA), so it is necessary to design a fast and accurate method to predict GFA. In this paper, four deep learning models of BidiRNN, BidiLSTM, Attention-BidiRNN and Attention-BidiLSTM are constructed by using recurrent neural network (RNN) and Attention mechanism, and the GFA of alloys is directly predicted by element proportion. After model selection and model evaluation through cross-validation, the prediction accuracy of the four models on the test set is 0.727, 0.796, 0.822 and 0.843, respectively, which has good generalization performance. Since amorphous alloys usually have high similarity to similar alloy systems, the attention mechanism can dynamically identify alloys with high similarity to the current prediction task. By weight matching, the feature extraction ability of the model is enhanced, and the prediction accuracy of Attention-BidiRNN and Attention-BidiLSTM is 9.05% and 4.7% higher than that of BidiRNN and BidiLSTM, respectively. Finally, two systems of CuZrAl and CuCeGa are predicted in this paper, and the reliability of the model is verified by experimental data. This realization of predicting GFA only by combination of elements is expected to provide important guidance for the development and preparation of novel amorphous alloys.

An exploratory study on biocompatible Ti-6Mn-4Mo alloy manufactured by directed energy deposition

Titanium is a widely used metal in biomedical applications due to its low toxicity, but its mechanical properties need to be tailored for different applications. Efforts are called for to search for effective and yet non-toxic elements to be alloyed with Ti to improve its strength. Fitting in this category, Mn and Mo are two such alloying elements. In this study, Ti-6Mn-4Mo alloy was manufactured by laser-directed energy deposition (DED) through in situ alloying of Ti, Mn, and Mo elemental powders. This study was intended to not only demonstrate for the first time the printability of the Ti-Mn-Mo ternary system by laser DED but also investigate the basic mechanical properties and corrosion resistance of the obtained alloy. Under the as-built condition, the alloy consisted mainly of ß phase, while after heat treatment it was transformed into α phase. The average ultimate tensile strength under as-built condition was 706.0 MPa, lower than similar alloys from conventional methods. However, the average hardness reached 421.1 HV for the as-built condition, much higher than the similar alloys made through conventional methods. On the other hand, the corrosion resistance of the obtained alloy was found to be relatively low compared to similar alloys produced with traditional methods. In addition, heat treatment was not able to significantly change the tensile properties or the corrosion resistance. In essence, the exploratory study indicates that the DED-produced Ti-Mn-Mo alloy could be deposited without cracks and major voids, and shows that its high hardness and modulus are attractive to applications for high wear resistance. However, further investigation is needed to improve strength, ductility, and corrosion resistance of the alloy.

Options for Improving Performance of Additively Manufactured Nickel-Base Superalloys for Gas Turbine Applications

Abstract Additive manufacturing (AM) has been increasingly used for gas turbine (GT) components over the last decade. Many different components can be successfully designed, printed, and used in the gas turbine. However, there still exist questions on the use of AM components in hot-section areas. These components are typically fabricated from nickel-base superalloys that are known to have superior mechanical properties at elevated temperatures (e.g., creep and fatigue). Research over the last decade has been primarily focused on the printability of nickel-base superalloys, and there still exists a gap in understanding the high temperature processing–structure–properties–performance relationships of these alloy systems. This study evaluates the effect of processing methods, such as laser-based powder bed fusion (LBPBF) and electron beam powder bed fusion (EBPBF), on the resulting microstructure and time dependent mechanical properties of a nickel-base superalloy (ABD®900). Material after each build was subsequently heat treated using both near-solvus (at or slightly below the gamma prime solvus temperature) and super-solvus (above gamma prime solvus temperature) conditions. Multistep aging was then carried out to produce a bi-modal distribution of gamma prime precipitates as is typical in similar alloys. Microstructure was evaluated in both the as-built and fully heat-treated conditions for each processing technique. Mechanical testing was conducted to evaluate the effects of AM build methods, microstructure, and heat treatment on high temperature mechanical properties. The results show that there are several methods which can be used to improve the performance of components built using AM. The creep testing results for ABD900-AM clearly show an improvement in properties (rupture life and ductility) at all test conditions compared to testing in the prior AM alloy of the same class. A super-solvus heat treatment improved creep rupture strength by ∼3× in the LBPBF material compared to the near-solvus heat treatment. These findings provide directions for future studies to advance the overall state of gas turbine technology by enabling ABD®900-AM material and other AM alloys to be used in more innovative hot-section components.

The effect of Mn content on a novel Al–Mg–Si-Sc-Zr alloy produced by laser powder bed fusion: The microstructure and mechanical behavior

Scandium is very expensive and limits the application potential of Sc containing alloys. A novel high-strength Al–Mg–Mn-Sc-Zr alloy was designed for reducing Sc. Multiple strengthening mechanisms were utilized for designing this alloy, especially for the solid solution strengthening which benefits from ultrahigh cooling. With the addition of Mn and Si, the strength of our alloy reaches comparable level of similar alloys while the Sc content is 40–60 % less than them. The effect of Mn addition on microstructure and mechanical properties were carefully studied. Near full-dense samples with relative density >99.88 % were obtained with the help of overlapping prediction model. The continuous Mg2Si network was observed with Si introduction and broken up with increasing Mn content. According to the tensile experiment results and corresponding calculations, it was considered that the thermal stability and the effect of precipitate strengthening was slightly deteriorated. However, obvious improvement of the tensile strength was observed with increasing Mn addition, and the ductility maintains in a certain range. After aging at 280 °C for 4 h, the sample of 1.4 wt% Mn exhibits the highest ultimate strength of 497.08 ± 7.22 MPa, and possesses a considerable ductility of 8.01 ± 0.34 %. The Portevin-Le Chatelier (PLC) effect was observed in stress-strain curves, which reflects a dynamic strain aging of mobile dislocations and solute atoms. After aging, the stress amplitude and waiting time of serration flow decrease obviously, because of the introduction of bypassing precipitates and reduction of diffusion time. Compared with other similar alloys, our alloy exhibited comparable yield strength and elongation, but considerable advantages in material costs resulting from lower Sc content. It will offer not only an idea for alloy design utilizing the ultra-high solid solubility of elements, but also a feasible way to further expand application field of high-strength Al-based alloys through reducing the material costs.

Tunable magnetocaloric effect towards cryogenic range by varying Mn:Ni ratio in all-d-metal Ni(Co)-Mn-Ti Heusler alloys

Cryogenic magnetic refrigeration is a highly efficient and environmentally friendly technique for gas liquefaction. However, refrigerant materials undergoing large magnetocaloric response at the interesting cryogenic range are dominated by critical elements (mainly rare-earth elements) which impedes practical applicability of such refrigeration systems. Therefore, there is a need for dedicated investigations on optimization of magnetocaloric response at cryogenic range by utilizing compositions that are rare-earth free. In this work, we synthesize the mechanically stable and rare-earth free, all-d-metal Ni35Co15Mn35Ti15 Heusler alloys and investigate the role of varying Mn:Ni ratio on the magnetostructural and magnetocaloric properties of the alloy system. The results of the microstructural characterization indicate homogenous composition for the investigated alloy series. As the Mn:Ni ratio increases from 1.01 to 1.10, the martensitic transition shifts from near-room temperature down to cryogenic region (120–140 K) while the magnetization of the austenitic phase remains unaltered. Isothermal entropy change as high as ∼ 13 J kg−1 K−1 at 1.5 T is achieved for the sample with the highest Mn:Ni ratio at the temperature region for natural gas liquefaction, which significantly surpasses the values previously reported in the literature for similar alloys. In addition to large magnetocaloric response, the martensitic transformation falls in an interesting temperature of the cryogenic region, paving the way for various low-temperature magnetocaloric applications.

Effects of filler on the microstructure and corrosion of similar and dissimilar gas inert tungsten arc welding aluminum alloys joints

Welding of dissimilar aluminum alloys has been widely used in many industrial applications. However, the selection of filler type still attracts significant interest in the welding research area. The present work concerns the effect of filler metal on the microstructure and corrosion of weld joints of dissimilar aluminum alloys. AA 5083 and AA 6082 alloys were welded by tungsten inert gas welding (GTAW) using filler metals ER 4043 and ER 5356. The microstructure observations and the corrosion test of the weld joints were carried out. Solidification cracks were observed in the ER 4043 weld zone, whereas defect-free joints were obtained using a mix filler welding process. A galvanic corrosion was observed on the boundary between the filler rod ER 4043 weld zone and AA 5083 base alloy. From the corrosion standpoint of view, the using of ER 4043 electrodes is not preferred for welding 5000 series aluminum alloys, whereas ER 5356 filler electrode is more favorable than ER 4043 filler electrode either for dissimilar welding of AA 5083 and AA 6082 alloys or individual welding of both aluminum alloys. No galvanic corrosion is observed between ER 4043 fillers and AA 6082 base alloy.

Microstructural mechanisms imparting high strength-ductility synergy in heterogeneous structured as-cast AlCoCrFeNi2.1 eutectic high-entropy alloy

The dual-phase AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) presents a promising solution to the strength-ductility trade-off dilemma, making it a highly desirable option for structural materials with vast potential applications. However, the relationship between the mechanical properties and the unique as-cast heterostructures needs to be further revealed. Here, we conducted in-situ tensile experiments of the as-cast EHEA to unveil the mesoscopic/microscopic microstructural mechanisms of strength-ductility synergy via investigating the dynamic real-time plastic deformation behaviors and crystallographic information evolution, as well as characterizing the deformed microstructures via transmission electron microscopy. The results indicate that the sequential dominant heterogeneous deformation induced hardening resulting from the incompatible plastic deformation between different types of heterogeneous microstructures is the primary source of its remarkable strength-ductility synergy. Moreover, the unique elongated lamellar microstructures of the as-cast EHEA offer numerous phase boundaries, and the growth twins in the face-centered cubic (FCC) phase generate abundant twin boundaries, all of which contribute to boundary strengthening and further enhance the strength and ductility of the as-cast EHEA. Furthermore, abundant cross-slip and dislocation substructures in the FCC phase provide strain hardening for as-cast EHEA, while body-centered cubic phase contributes to the high strength through precipitation hardening. Consequently, the heterostructure induced multiple strengthening mechanisms are responsible for the high strength-ductility synergy in the as-cast EHEA. The present work provides a new perspective to explain the strength-ductility synergy of similar heterogeneous structured alloys.

In situ synthesis and regulation of spherical Ti6Al4V powder by calciothermic self-propagating metallurgy

In this paper, spherical Ti6Al4V alloy powder was successfully prepared by calciothermic self-propagating rapid reaction method, in which TiO2, V2O5, Al and Ca were used as raw materials. The reduction reaction can be completed in minutes with no need for any external energy and additives in the reaction process. By investigating the influence of the additives, the amount of reductant Ca added, the reaction pressure and the particle size of Ca, on the composition as well as the morphology of the product, the optimal alloy powder with an low oxygen content of 0.21 wt% was obtained, whose average particle size and specific surface area were 15.28 μm and 0.284 m2/g respectively. Moreover, this research implied the adiabatic temperature of the system and the liquid Ca are the main factors that pose influence to the powder morphology during sintering-reduction-spheroidization-solidification process. Compared with the traditional Ti6Al4V alloy powder preparation process, this process stands out with characteristics of high purity, short production cycle and environmental friendliness, which show high commercialization potential for industrial preparation of Ti6Al4V and similar alloy powders.

Prediction of Axial Force on Dissimilar Aluminum Alloys Friction Stir Welding Using Design of Experiment

Friction stir welding (FSW) has become very popular for joining similar or dissimilar aluminum alloys. The heat used for this welding process is caused by friction between the welding tool and the workpiece which the axial force, the main parameter for heat generation, plays a very important role. Insufficient heat during welding will result in defective workpieces. This research is aimed to predict the axial force from the relevant factors of the FSW of dissimilar materials (aluminum alloys AA2024-T3 and AA6061-T6). The 23 full factorial design with center point was used for this experiment that consisted of 3 main factors: 1) rotation speed (rpm), 2) welding speed (mm/min), and 3) pin geometry each factor has 2 levels and 2 replications with the total of 20 experiments. The axial force data of each experiment were collected using a stationary dynamometer which obtained the data acquisition every 0.1 seconds (frequency of 10 Hz). The results from the design of experiment were analyzed by statistical method at the significance level of α = 0.05 which found that the significance and the optimum value of the main factors were rotation speed of 1500 rpm, welding speed of 35 mm/min, pin geometry of tri flat threaded, and the 2-way interaction between rotation speed and pin geometry. Furthermore, the prediction of the average axial force value on dissimilar aluminum alloys obtained from the specified parameters equals 478.91 N.

Multi-objective optimization of process parameters during friction stir welding of similar AA6061 using MOORA

This work is an attempt to select the optimum process parameters for friction stir welding of similar AA6061 aluminum alloy based on multiple criteria decision-making approach. The friction stir welding experiments have been conducted according to the orthogonal L9 array and the chosen input parameters are tool rotational speed, feed, and tilt angle. The responses measured are tensile strength, hardness, and % of elongation of welded joint. The multi-criteria decision-making technique namely multi-objective optimization based on the ratio analysis (MOORA) is used to find the optimum process parameters combination. The optimum conditions are tool rotational speed of 1120 rpm, feed of 30 mm/rev and tilt angle at 1 o.

Experimental Analysis on Ultrasonic Resistance Spot Welding of Aluminum Alloys

A recently developed hybrid joining process known as ultrasonic resistance spot welding (URW) was used on various pairs of similar and dissimilar aluminum (Al) alloys with different thicknesses, including AA5182–AA5182, AA6111–AA6111, AA7075–AA6111, and AA7075–AA5182, and comprehensively studied. Compared to conventional resistance spot welding (RSW), URW of the alloys showed consistently enhanced mechanical behavior in lap shear and crosstension tests. This can be attributed to the multiple perspectives on microstructure improvements. For different stacks of Al alloys and welding conditions, nugget formation was promoted with a larger nugget size in URW. In the nugget center, ultrasonically assisted (UA) vibration facilitated the formation of an equiaxed crystal zone. At the nugget boundary, URW showed a narrower coarse columnar zone and partially melted zone, which are associatedwith the lowest hardness in the weld. Specifically in dissimilar Al welds, UA vibration moved the nugget more centered toward the weld interface. These microstructure improvements indicated UA vibration can homogenize temperature and elemental distribution, which modifies solidification behavior.

Microstructure and mechanical behavior of similar and dissimilar AA2114 and AA7075 aluminium alloy joints using fusion welds

Joining of aluminium and its alloys are always a major challenge to welding community because of high thermal conductivity, coefficient of linear expansion, affinity to combine with oxygen and sensitive to hot cracking. Ample of researches carried out to address above issues. The selected investigation aimed at one such attempt to combine AA2114 and AA 7075(AA2XXX and AA7XXX series promises a lot in aircraft applications) in all possible ways i.e. similar and dissimilar by adopting TIG (Tungsten Inert Gas) and CMT (Cold Metal Transfer) welding. After series of trials, all the combinations welded successfully and tensile specimen as per ASTM E8 machined. While performing mechanical testing, all specimens failed along the interface of weld zone and AA2114 side irrespective of TIG/ CMT dissimilar welding. This is accounted to softening in the heat affected zone of selected heat treated alloys i.e. AA2114 and AA7075. Among all the fabricated weld joints AA 2114-AA7075 specimen showed highest ultimate tensile strength of 247 MPa using filler ER 4043 alloy with CMT welding. Yielding of above outcome may be due to segregation of alloying elements (acts barrier to dislocation motion) and low concentrated heat input (favoring maximum extent of finer dendritic equiaxed grains).XRD-report revealed the presence of Zn, Cu, Mg elements in the intermetallic to have strength in CMT dissimilar CMT weldment. SEM analysis report on dissimilar joints of both TIG and CMT exemplifies the presence both dimples and flakes, which led to the ductile–brittle mixed mode nature of failure.

Experimental Analysis of Machining Parameters In Turning of Aluminum 7075

High-Speed Machining (HSM) of aluminum alloys represents a critical area in manufacturing industries, including automotive, aerospace and consumer electronics. This research presents an in-depth investigation into the effects of key process parameters on the HSM of Aluminum 7075, a high-strength alloy with superior mechanical properties. Utilizing the central composite design of Response Surface Methodology (RSM), the study scrutinizes the impact of process parameters, including cutting speed, feed, depth of cut and tool nose radius on surface roughness. The findings reveal feed and nose radius as primary factors influencing surface roughness while cutting speed and depth of cut play secondary roles. This comprehensive analysis contributes to the knowledge base for efficient machining practices and lays the groundwork for future optimization strategies. It also underscores the necessity for further research into understanding the intricate dynamics of machining parameters to enhance operational efficiency and product quality in the machining of Aluminum 7075 and similar alloys.

Design of bimorphic-bimodal microstructure in titanium alloys by semi-solid sintering

We have innovatively achieved bimorphic-bimodal microstructures (BBMs) by semi-solid sintering of TiNbNiCu(Al/Sn) amorphous alloy powders. The BBM contains equiaxed ultrafine-grain matrix, which inherits crystallized equiaxed microstructure after solid sintering, of fcc MTi2 (M = Cu, Ni) embeded into bcc β-Ti, accompanied by isolated regions with coarse β-Ti surrounded by ultrafine-grain fcc MTi2 shell, which originate from fast growth of crystallized β-Ti formed during solid sintering and rapid cooling of fcc MTi2 melt during semi-solid sintering. Resultantly, the BBMs exhibit high an ultimate compressive strength of 2567 MPa and a large plastic strain of 38.1%, superior to those of similar titanium alloys fabricated by melt solidification. The excellent mechanical properties are attributed to the multiplication of slip bands, which are formed in bcc β-Ti phase regions and intercepted by fcc MTi2 phases in the BBM titanium alloys. We anticipate that our work could provide a new strategy for designing lightweight and high-performance materials.

Microstructural analysis of cooling tank-assisted hybrid friction stir welded aluminium alloys: a novel approach

The friction stir welding process is a solid-state technique for joining similar and dissimilar alloys. The advanced fixture was designed and fabricated for welding of the aluminum plate by a hybrid fabricated fixture on a vertical milling center. The storage tank was designed and attached at the bottom of the base plate of the fixture. The three different cooling media used in the cooling tank as air, water, and coolant. The welded samples were examined for mechanical and metallurgical performance. The optimization of process parameters was done for the tensile Test as output. The coolant as a fluid in the tank results in maximum tensile strength at 500 rpm. The microstructural characterization of the heat-affected zone was also done. The weld thinning and quenching are the main problems of direct cooled FSW. This problem is not found in the indirect cooled FSW welding method. The storage tank provided uniform heating and cooling during welding that reduced the thermal quench and microstructural problems. The SEM and EDX mapping images showed the effect of different cooling media on the FSW samples. The microhardness was analyzed to identify different microstructural zone and the hardness of welded part.