Description:
F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)

COMPLETE SPECIFICATION
(See section 10 and rule 13)

TITLE
HIGH ENTROPY ALLOY-REINFORCED SS410 COMPOSITION

INVENTORS
NACHIMUTHU, Radhika – Indian Citizen
No. 309, Raja Brindavan Nagar, Kurumbapalayam Road, Madukkarai
Coimbatore, Tamil Nadu 641105
SINGH, Aman – Indian Citizen
142, Shiv Shakti Nagar Colony, Padari Bazar
Gorakhpur, Uttar Pradesh 273014
SANUBOINA NADAMUNI, Kishan – Indian Citizen
No. 10, 9th Avenue, A Sector, Siva Sakthi Nagar, Annanur PO
Chennai, Tamil Nadu 600062

APPLICANTS
AMRITA VISHWA VIDYAPEETHAM
Coimbatore Campus, Coimbatore- 641112,
Tamil Nadu, India

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:

HIGH ENTROPY ALLOY REINFORCED SS410 COMPOSITION
CROSS-REFERENCES TO RELATED APPLICATION
[0001] None.
FIELD OF THE INVENTION
[0002] The disclosure generally relates to materials and, in particular to improved corrosion and wear resistant stainless steels.
DESCRIPTION OF THE RELATED ART
[0003] In the steel industry, stainless steels have wide range of applications in engineering and medical sectors through its excellence in mechanical properties, sufficient weldability, and durability in erratic environments. The stainless steel grade 410 (SS410) is one among the martensitic group of steels and is preferred for manufacturing surgical and dental instruments, bearings in aerospace industries, storage tanks for steam and gas turbine components in nuclear applications. The features of SS410 including higher hardness, tensile properties, wear resistance, fatigue, and creep behaviours make them an effective utilization in engineering industries.
[0004] For synergistic applications, steel alloys could be used as steel-metal matrix composites and nanofiller composites. However, production of such composites is highly challenging because of poor wettability of particles, ductility, particle fragmentation, porosity, and variation in the thermal coefficient of reinforcement materials. A newly developed material, High Entropy Alloy (HEA) gets more significance by its unique characteristic nature in the past few years [9]. The HEA is a solid solution alloy having five or more principal elements of equal or unequal atomic percentile. The HEA acts as an effective reinforcement driven by its four core effects such as the cocktail effect, high-entropy effect, sluggish diffusion, and lattice distortion.
[0005] The invention discloses a new particle-reinforcedSS410 alloy based on HEA particle reinforcement.
SUMMARY OF THE INVENTION
[0006] The disclosure relates to a high entropy alloy (HEA)-reinforced SS410 alloy composition exhibiting enhanced wear resistance and hardness. The novel alloy comprises an SS 410 matrix containing 8-15% of AlSiBeTiV HEA by weight dispersed within the matrix. The AlSiBeTiV HEA includes equiatomic proportions of Al, Si, Be, Ti, and V, and exhibits face-centered cubic structure with X-ray diffraction peaks at 30.0, 35.42, 44.48, 62.55 and 82.16.
[0007] In various embodiments, the novel composition has grain size of the matrix in the range 0.4 - 2 µm. The hardness of the alloy is 450 HV100 or more and increase in tensile strength of 45% or more, and exhibits wear resistance of 35% or more over the base SS410 alloy.
[0008] The invention includes a method (200) of producing a AlSiBeTiV HEA dispersed SS410 alloy. The method comprises producing (202) AlSiBeTiV HEA by charging (202a) equiatomic proportions of Al, Si, Be, Ti and V in a ball mill, and ball milling (202b) the charge for 20 hours milling duration at a ball-to-powder weight ratio of 10:1 and 250 rpm milling speed to produce the HEA.
[0009] Further steps involve providing (204) a SS410 alloy plate, preparing (206) a groove within the plate, the groove having a top width and a height, filling (208) the groove completely with the AlSiBeTiV HEA. In the next step, the HEA powder added to the groove is compacted using a pinless FSP tool. The friction stir processing (FSP) (210) of the plate with filled groove is then done over a center line of the groove, The FSP in various embodiments is done using a tool having diameter 4 times a width of the groove. In various embodiments, the tool may be provided with a centrally located tapered pin of diameter equal to the groove width at an end thereof. The friction stir processing is carried out using a specified tool rotation speed, a predetermined traverse speed and a predetermined downward force to obtain the AlSiBeTiV HEA dispersedSS410 alloy. In various embodiments, the alloy may be obtained within a friction stir processed zone equal to the diameter of the tool.
[0010] In various embodiments, the ball milling of the HEA powder in step 202b is done using compatible grinding media with tungsten carbide balls and milling vial. In various embodiments, the groove is of V-shape, semicircular shape, oval shape or trapezoidal shape. In various embodiments, the groove is a curved groove or a linear groove.
[0011] This and other aspects are described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention has other advantages and features, which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:
[0013] FIG. 1A and FIG. 1B illustrate a method of fabricating AlSiBeTiV HEA reinforced-SS410 alloy.
[0014] FIG. 2A illustrates XRD pattern of AlSiBeTiV HEA produced using CuK? radiation, showing FCC structure of the HEA.
[0015] FIG. 2BillustratesXRD pattern of the HEA-reinforced SS410 alloy.
[0016] FIG. 3A illustrates macro section of the friction stir processed zone having the HEA-reinforced alloy.
[0017] FIG. 3B illustrates grain size distribution in the friction stir processed zone, illustrating the grain refinement.
[0018] FIG. 3C illustrates inverse pole figure (IPF) of the grain structure of the SS410 alloy.
[0019] FIG. 3D illustrates a micrograph of the SS410 alloy showing grain Grain boundaries.
[0020] FIG. 4illustrates microhardness profile across the HEA-reinforced zone.
[0021] FIG. 5 illustrates stress-strain profiles of the friction stir processed HEA-reinforced SS410 alloy vs. friction stir processed unreinforced SS410.
[0022] FIG 6illustrates applied load vs. wear rate for HEA-reinforced SS410 alloy.
[0023] FIG 7 illustrates sliding velocity vs. wear rate for HEA-reinforced SS410 alloy.
[0024] FIG. 8 illustrates sliding velocity vs. coefficient of friction for HEA-reinforced SS410 alloy.

DETAILED DESCRIPTION OF THE EMBODIMENTS
[0025] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.
[0026] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of “a”, “an”, and “the” include plural references. The meaning of “in” includes “in” and “on.” Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.
[0027] The invention discloses a novel high entropy alloy-reinforced SS410 composition, and method of fabricating the same. The high entropy alloy (HEA)-reinforced SS410 alloy composition is configured to exhibit enhanced wear resistance and hardness compared to the unreinforced alloy. In various embodiments, the alloy comprises a SS 410 matrix containing 8-15% of AlSiBeTiV HEA by weight dispersed within the matrix. The AlSiBeTiV HEA includes equiatomic proportions of Al, Si, Be, Ti, and V. The AlSiBeTiV HEA exhibits face-centered cubic structure with X-ray diffraction peaks at 30,35. 42,44.48, 62.55 and 82.16.
[0028] In various embodiments, the novel composition is configured to have a grain size of the matrix in the range 0.4 - 2 µm, thereby conferring enhancement of mechanical properties. In various embodiments, the hardness is configured to be 450 HV100 or more. In various embodiments, the refined grain size is configured to give an increase in tensile strength over the base SS410 alloy of 45% or more. In various embodiments, the novel alloy is configured to exhibit wear resistance of 35% or more over the base SS410 alloy.
[0029] In various embodiments, a method (200) of producing a AlSiBeTiV HEA dispersed SS410 alloy, is disclosed with reference to FIG. 1A and 1B. The method includes the step of producing (202) AlSiBeTiV HEA. The method of producing AlSiBeTiV HEA includes charging (202a) equiatomic proportions of Al, Si, Be, Ti and V in a ball mill and ball milling (202b) the charge for 20 hours milling duration at a ball-to-powder weight ratio of 10:1 and 250 rpm milling speed to produce the HEA.
[0030] In the next step (204) a SS410 alloy plate is provided. A groove is then prepared (206) within the plate. In various embodiments, the groove may have a suitable cross-sectional shape such as V, a trapezoidal shape, a semicircular or oval shape. In one embodiment, the groove may be trapezoidal with a bottom width and a top width greater than the bottom width. The groove is provided of a height suitable for effective friction stir processing of the alloy.
[0031] The next step involves filling (208) the groove completely with the AlSiBeTiV HEA, followed by friction stir processing (FSP) (210) the plate with filled groove over a center line of the groove. The friction stir processing in various embodiments may be done using a tool having diameter 4 times a width of the groove. In various embodiments, the tool may have a centrally located tapered pin of diameter equal to the groove width at an end thereof. In various embodiments of the method, the friction stir processing is carried out using a specified tool rotation speed, a predetermined traverse speed and a predetermined downward force to obtain the AlSiBeTiV HEA dispersed SS410 alloy within the friction stir processed zone equal to the diameter of the tool.
[0032] In various embodiments of the method, the step of compacting (209) the HEA powder added to the groove using a pinless FSP tool, may precede the FSP (210).In various embodiments, the ball milling the HEA powder may be done using a suitable ball milling apparatus. In one embodiment, the ball mill may utilize tungsten carbide balls in a tungsten carbide milling vial.
[0033] In various embodiments of the method, the groove may be a linear groove or a curved groove. The shape of the groove may be tailored to match a shape of the component. For example, a valve seat of circular shape may be processed to provide a hard surface along the mating circular surface, using an annular groove. Linear components and surfaces may be produced using a linear groove.
[0034] The invention has multiple advantages as set forth herein. The AlBeSiTiV HEA powder is a novel elemental combination in the HEA design-based system, where the combined density of the quinary elements is less than 6 g/cc which makes them a lightweight HEA. The elements chosen are economically feasible and offer enhanced properties at relatively lower cost. The AlBeSiTiV HEA exhibits stable single-phase FCC structure with a sharp diffraction angle which improves wear and corrosion resistance. Being lightweight HEA, AlBeSiTiV HEA can be used as a reinforcement to attain better strength to weight ratio. The AlBeSiTiV HEA can be exclusively applicable for bearings, valve seats, turbine blades, compressor components in aerospace industries, and steam turbine buckets.
[0035] EXAMPLES
[0036] Example 1: Materials and Methods
[0037] A novel material combination (Al, Si, Be, Ti, and V) under the lightweight categories was used as multifunctional elements in HEA. Equiatomic proportions of Al, Si, Be, Ti, and V were taken to prepare HEA particles by the ball milling process. The significant process parameters such as 250 rpm milling speed, 20 hrs milling time, 10:1 ball-to-powder weight-ratio, tungsten carbide balls as grinding media, and tungsten carbide milling vial are used. The SS410 steel plate was commercially procured from industry and the elemental composition of SS410 in weight % is listed in Table 1.
[0038] A 10 wt.% AlSiBeTiV HEA was used to reinforce on SS410 alloy through friction stir processing. The effective surface composites are obtained using trapezoidal grooves with a dimension of 4 mm at the top, 2 mm at the bottom, and a height 4 mm at the centre of a 100x50x6 mm plate. The improved hardness and tensile strength of 518 HV and 896 MPa respectively are attained in the HEA-processed sample, which is 47 % and 49.8 % higher than the processed substrate. Additionally, the wear resistance of HEA-processed samples is increased by 39.34%, 33.63%, and 39.75% under the applied load, sliding distance, and sliding velocity respectively over the processed substrate.
[0039] The plate was cut by wire-cut electric discharge machining (EDM). Initially, a trapezoidal slot with a taper ratio of 2:1 and a depth of 4 mm was made at the middle of the base plate by the wire-cut EDM process.
[0040] The machined samples were cleaned with acetone to prevent contamination by oil or other impurities. The synthesized AlSiBeTiV HEA powder was then added into the groove and compacted by a pin-less FSP tool, as illustrated in FIG. 1B. Finally, the FSP was carried out with a tapered cylindrical tool made of tungsten carbide with dimensions 16 mm, 4 mm, and 4.5 mm shoulder diameter, pin diameter, and pin length respectively. The heat is generated on the surface of the base plate by the friction of the non-consumable rotating tool. FSP does not require any external heat or produce any hazardous rays and fumes during the process.
[0041] The refined grains are homogeneously distributed over the base plate through a one-step process compared to other solid-state processing methods. Grain size of the processed sample is controlled by induced frictional heat via specified process parameters, and tool design. FSP was carried out with optimal parameters of 900 rpm rotational speed, 20 mm/min traverse speed, and 10 kN downward force. The sequence of producing HEA particles reinforced with SS410 steel plate through FSP is illustrated in FIG. 1B.
Table 1 Chemical composition of SS410 steel
Element C Cr S Ni Si P Mn Fe
% 0.15 12.80 0.03 0.75 1.0 0.04 1.0 Balance
[0042] The morphological evaluation of synthesized AlSiBeTiV HEA powder and stir zone of processed samples was conducted by SEM (ZEISS Gemini SEM 300). X-Ray Diffraction (XRD) was used to analyze the phase structure of HEA powder as shown in FIG. 2Aand HEA-processed sample, as shown in FIG. 2B. To verify the presence of principal elements in the HEA powder and HEA-processed sample, Energy Dispersive x-ray Spectrometer (EDS) analysis was carried out. The grain reduction and its distribution over the stir zone in the HEA- processed sample were evaluated by Electron Backscatter Diffraction (EBSD). A Vickers hardness test (Mitutoyo) was performed with a diamond pin indenter to find the micro hardness of processed samples. The hardness test was conducted as per ASTM 384 with a load of 100 gf and a holding time of 15 s. The tensile behavior of processed samples was analyzed through an Ultimate tensile test machine (Tinius Olsen). The tensile test samples are prepared according to ASTM E8. To carry out the wear analysis of processed samples, the pin-on-disc apparatus (TR-20LE- PHM-200 model) was used as per ASTM G99. An EN32-steel disc with a hardness of 65 HRC was used as the counterpart. The tribological behaviour of processed samples was monitored at ambient temperature. The wear test of processed samples was conducted at the applied load (10–40 N), sliding distance (500–2000 m), and sliding velocity (0.5–3.5 m/s). The initial and final weight of wear samples was measured by single pan electronic weighing machine. The wear samples are dried and cleaned with acetone solution before taking the initial weight of samples to prevent impurities and moisture content [37]. Wear rate and Coefficient of Friction (COF) are calculated by the relations (1) and (2) mentioned below. The wear mechanism of worn surfaces was analysed by morphological evaluation.
Volumetric wear rate = Weight loss of wear samples / Sliding distance (1)
Coefficient of Friction = Frictional force /Applied load (2)
[0043] Example 2: Evaluation of FSP SS410 Alloy
[0044] Macro cross section of the FSP zone is shown in FIG. 3A.Grain refinement of the HEA-processed sample is a prime feature of FSP for enhancing strength. The grain size and distribution of the HEA- processed sample are evaluated by EBSD. The distribution of the grain size in the stir zone is shown in FIG. 3B. The crystallographic direction exhibits more distinct grains than the rolling direction as evidenced by the mapping of the Inverse Pole Figure (IPF) in FIG. 3C. The refined grain structure is observed on the HEA-processed sample by dynamic recrystallization and severe plastic deformation during FSP, as shown in FIG. 3D.
[0045] The microhardness profile of the HEA-processed sample and the processed base plate is shown in FIG.4. The HEA-processed sample exhibits higher microhardness in the range of 518 HV. The HEA-processed sample produce 47% higher microhardness than the processed base plate. The refined grain structure of the processed samples causes improved microhardness according to the Hall-Petch relationship.
[0046] The tensile strength of the HEA-processed sample and processed base plate are illustrated by the stress-strain graph (FIG.5). The UTS of the HEA-processed sample is observed to be 896 MPa and 49.8% higher than the processed base plate. The refined grains of processed samples attribute to higher tensile strength by the grain strengthening effect. The grain reduction is carried by the mechanical string action of the FSP tool and the combined effect of effective process parameters. The quenching effect through induced temperature by friction between the tool and work sample also contributes to grain refinements. The grain size reduction in the stir zone offers improved tensile properties, which is one of the major features of FSP.
[0047] The refined grains of processed samples attribute to higher tensile strength by the grain strengthening effect. The grain reduction is carried by the mechanical string action of the FSP tool and the combined effect of effective process parameters. The quenching effect through induced temperature by friction between the tool and work sample also contributes to grain refinements. The grain size reduction in the stir zone offers improved tensile properties, which is one of the major features of FSP. Dynamic recrystallization and severe plastic deformation during the FSP attributed to effective grain refinement in the processed samples. The reinforced HEA particles with base plate also contribute to the enhanced tensile strength of the processed
[0048] Wear rate analysis of the processed samples: The effect of process parameters such as applied load, sliding distance, and sliding velocity on the wear rate and COF of the processed samples are shown in FIGs. 6–8. The wear rate and COF of both processed samples are increased by the addition of applied load at a constant sliding distance of 2000 m and velocity of 3.5 m/s as illustrated in these figures. The HEA-processed sample exhibits a minimum wear rate of 2.456 × 10-3 mm3/m at 10 N and the trend increases linearly up to 30 N with a 24.42% increase in the wear rate. The COF also increased from 0.331 to 0.456 with the increment in applied load up to 30 N in the HEA-processed sample. The wear rate and COF of the HEA processed samples decreased by 27.48% and 24.56% than the processed unreinforced base plate.
[0049] The applied load contributes a more dominant role in wear analysis. The formation of an oxide layer at a high sliding distance and velocity protects the samples against wear. The barrier effect, load-bearing capacity, improved microhardness, and metallurgical bonding of HEA improved the wear resistance of the HEA-processed sample.
[0050] Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed herein. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the system and method of the present invention disclosed herein without departing from the scope of the invention, which should be as in the appended claims.

, Claims:We claim:
1. A high entropy alloy (HEA)-reinforced SS410 alloy composition exhibiting enhanced wear resistance and hardness, comprising:
an SS 410 matrix containing 8-15%ofAlSiBeTiV HEA by weight dispersed within the matrix.

2. The composition as claimed in claim 1, wherein the AlSiBeTiV HEA includes equiatomic proportions of Al, Si, Be, Ti, and V.

3. The composition as claimed in claim 1, wherein the AlSiBeTiV HEA exhibits face-centered cubic structure with X-ray diffraction peaks at 30.0,35.42,44.48, 62.55 and 82.16.

4. The composition as claimed in claim 1, with grain size of the matrix in the range 0.4 - 2 µm.

5. The composition as claimed in claim 1, wherein the hardness is 450 HV100 or more and increase in tensile strength over the base SS410 alloy of 45% or more.

6. The composition as claimed in claim 1, exhibiting wear resistance of 35% or more over the base SS410 alloy.

7. A method (200) of producing a AlSiBeTiV HEA dispersedSS410 alloy, comprising
producing (202) AlSiBeTiV HEA by:
charging (202a) equiatomic proportions of Al, Si, Be, Ti and V in a ball mill; and
ball milling (202b) the charge for 20 hours milling duration at a ball-to-powder weight ratio of 10:1 and 250 rpm milling speed to produce the HEA;
providing (204) a SS410 alloy plate;
preparing (206) a groove within the plate, the groove having a top width and a height;
filling (208) the groove completely with the AlSiBeTiV HEA;
friction stir processing (FSP) (210) the plate with filled groove over a center line of the groove, wherein the friction stir processing is done using a tool having diameter 4 times a top width of the groove with a centrally located tapered pin of diameter equal to the top width at an end thereof, wherein the friction stir processing is carried out using a specified tool rotation speed, a predetermined traverse speed and a predetermined downward force to obtain the AlSiBeTiV HEA dispersed SS410 alloy within a friction stir processed zone equal to the diameter of the tool.

8. The method as claimed in claim 7, comprising compacting (209) the HEA powder added to the groove using a pinless FSP tool, prior to FSP.

9. The method as claimed in claim 7, wherein the ball milling the HEA powder is done using tungsten carbide balls in tungsten carbide milling vial.

10. The method as claimed in claim 7, wherein the groove is of V-shape, semicircular shape, oval shape or trapezoidal shape.

11. The method as claimed in claim 7, wherein the groove is a curved groove or a linear groove.

Dr V. SHANKAR
IN/PA-1733
For and on behalf of the Applicants