Study On Microstructure And Mechanical Properties Of Pt-20Rh Alloy Reinforced By Oxide Particles

Platinum and its alloys have excellent corrosion resistance,high temperature creep resistance,high melting point and good formability,which not only are structural material with excellent performance,but also the unique features of the functional materials,is the only one can used in the atmosphere at 1800?.Pt materials are essential for the preparation of nitric acid catalytic materials in industrial processes.Platinum and its alloys play an important even irreplaceable role in automotive,electronic and electrical,chemical,petrochemical,glass manufacturing,aerospace,military,jewelry and other fields.Since the Pt particle will rapidly grow at high temperature,its strength will reduce at high temperature.Therefore Pt can not meet the use requirement of glass fiber wire drawing bushing,forming flat panel display glass forming channel,preparation of nitric acid industrial catalysis net platinum products in high temperature,corrosion resistance,size stability and other aspects.Solid solution strengthening and dispersion strengthing can improve the properties of the alloy greatly.Bushing,channel,catalytic network,thermocouple,jewelry and other platinum molding products are related to a large number of welding process.Thus,welding quality has great influence on product performance,service life.It has important scientific value and engineering application value that study the welding microstructure and properties of platinum and its alloys,especially which have been strengthed by main preparation methods of dispersion strengthening and solid solution strengthening.In this paper,by adding different amounts of Zr and Y elements to platinum rhodium alloy,through the alloy melting,powder preparation,internal oxidation sintering,forging and rolling forming,dispersion strengthening of Pt-20 Rh sheet were prepared.The thin plates were welded by manual argon arc welding.Microstructure and mechanical properties were study on the dispersion strengthening Pt-Rh alloys with different contents.The results show that the dispersion strengthening phase in the alloy is oxide particles of Zr and Y.Metallographic corrosion to rolled Pt-20 Rh alloy is very difficult.The effect of conventional electrolytic corrosion is poor,while satisfying effect can be obtained after corrosion in boiling aqua regia for 15-30min/50-60?.The corrosion time and temperature depends on the alloy composition and microstructure.The argon arc welding of Pt-20Rh-x Zr-0.015 Y alloy sheet can be obtained with smooth surface,there are not defect both inside and outside of weld.A thin black oxide layer formed on the surface of the weld,which increase the coverage area with the added amount of Zr increases.After annealing at 1150 /20 min,the microstructure of the rolled alloy was recovered and a small amount of re crystallization was observed.The original crystalline grains,flat and recrystallized recrystallized grains were rolled in the TD-ND plane.With the increase amounts of Zr,more oxide particles can be formed,which results in the effect of grain boundaries on the grain growth,the grain size becomes finer,the volume fraction of recrystallized grains decreases,and the grain refinement.In the process of welding joint(weld nugget)WNZ occurred in the central area is the remelting,coarse equiaxed crystal,(near the fusion zone)TMAZ area is coarse columnar crystals,HAZ(heat affected zone)the recovery and recrystallization and grain growth,different content of Zr in the average grain size of platinum rhodium alloy 5.6?m-12?m.The grain size of Pt-20 Rh alloy is 40.3?m TMAZ without adding strengthening elements.There is no obvious separating line between HAZ and WNZ.The RD-TD crystal grains in the weld zone of Pt-20Rh-0.3Zr-0.015 Y alloy are symmetrically distributed in the center of the weld,and within two fusion lines are columnar crystals with different orientations,and the large diameter equiaxed grains are outside the fusion line of two.The phase change of Pt-20 Rh alloy at 700-800?.The tensile of Pt-20Rh-xZr-0.015 Y alloy after welding under normal temperature,tensile strength of 0.3Zr(?b)and yield strength(0.2 sigma)were the highest value of 452 MPa and 222 MPa.The addition of Zr,the formation of more oxide enhanced phase hindering the movement of dislocation that improve the strength of alloy.And the elongation decreases since stress concentration.The elongation rate(?)is the maximum value of 20.3% without adding Zr alloy.The diffusion of materials becom more easily,the deformation mechanism increases,and the strengthening mechanism normal temperature at 1000?.Therefore,comparing properties of room temperature the tensile mechanical properties is significantly reduced at 1000?.0.3Zr alloy ?b,?0.2 was highest(127MPa,112MPa).The maximum value of ? is 9% without adding alloy Zr.With the increase of Zr,the variation trend of strength and elongation is consistent with that at room temperature.The tensile fracture of Pt-20Rh-x Zr-0.015 Y alloy is ductile fracture at room temperature,which contained by a large number of dimples.Second phases will hinder dislocation movement,stress concentration,micro voids become the source,micro voids grow together to form dimples.When the content of Zr increased,the dimples is more and depth.Particle in the bottom of the dimple appears gradually increased(it is oxides of Zr and Y through EDS analysis).Tensile fracture of alloy powder metallurgy appear characteristics of intergranular fracture and brittle fracture,tear ridges and dimples disappeared at 1000?.Pt-20 Rh alloy section containing a large number of dimples was ductile fracture,delta reached 22%.The weld surface of Pt-20Rh-0.15Zr-xY alloy is smooth and free of defects and has good weldability.The upper surface and the lower surface of the weld WNZ near the fusion line are covered by a black layer that was formed by second phase.After annealing at 1150 /30 min,the grain size of the base metal was recovered and a small amount of recrystallization was formed.From the center of the weld zone to base area,the grain changed from coarse equiaxed to elongated columnar crystal,larger size of recrystallized grains and fine filamentous or flat rolled grain successively.The grain size decreases,the average diameter of the HAZ grains between 5.1-7?m.The microstructures of the welded joints with different Y content were little different.The ?b,?0.2 are highest with 413 MPa and 193 MPa respectively at room without Y of Pt-20Rh-0.15Zr-x Y.The ? is best with 0.05Y(13.5%).The alloy without adding Y has hightest ?b(106MPa).The ?0.2 and ? of the alloy adding 0.05%Y have are maximum value(87MPa,6.3%).The tensile mechanical properties of different Y have little differences at room temperatures and 1000?.Compared with the Pt-Rh alloy after casting,the tensile strength of Pt-20Rh-0.15Zr-xY alloy was increased by about 30% and the elongation was reduced by about 73%.