Research On Mechanical Properties And Wettability Of Pt-20Rh Alloy Dispersion Strengthened By Oxide

Platinum plays an irreplaceable role in the chemical,glass and other industries,due to its excellent high temperature stability and chemical inertness.For example,in the modern industry,platinum is the irreplaceable main material of wire-drawing bushing for the production of glass fiber wire drawing drain plates and platinum tubes for the production of flat panel display glass.Under the conditions of high temperature,pure platinum grains will grow and mechanical properties will be greatly reduced which make it difficult to meet increasingly stringent service performance requirements.Improving the performance of platinum alloys at room temperature and high temperature is critical to their application.Research and engineering practice at home and abroad showed that solid solution strengthening and dispersion strengthening are the most effective method to improve the room temperature and high temperature performance of platinum alloys.This paper focuses on the microstructure,mechanical properties,glass droplet wettability and welding properties of Pt-20Rh dispersion strengthened by ZrO₂ and Y₂O₃ particle.The main works and research results are as follows:（1）Pt-20Rh dispersion strengthened by ZrO₂ and Y₂O₃ particle samples were designed and prepared.1 mm thickness Pt-20Rh dispersion strengthened by different contents of oxide particle were prepared by smelting,electric spark plasma ablation milling,internal oxidation-sintering,high temperature forging,cold rolling,annealing and other processes.Welded joint samples were prepared by argon arc welding.（2）The test analyzed the tensile properties of the dispersion-strengthened Pt-20Rh alloys sheet in the rolling direction.The results show that with the increase of the content of Zr and Y,the yield strength,tensile strength and work hardening rate of the alloys at room temperature and 1000°C increased apparently,and the ductility decreased slightly.The experimental results at room temperature and 1000°C were in good agreement with the theoretical results based on the Orowan formula and the Arzt-R（?）sler-Wilkinson model,indicating that oxide particles such as ZrO₂ are the main dispersion strengthening phase.（3）TEM and HRTEM were used to observe the microstructure of the dispersion-strengthened Pt-20Rh alloys,and the size and crystal structure of the ZrO₂particles were analyzed.Scanning electron microscope electron backscatter diffraction（EBSD）analysis was used to characterize the matrix structure of the alloys.The composition of ZrO₂particles was studied by using energy dispersion spectroscopy（EDS）of JEM-2100.It was found that the Pt-20Rh matrix was a recovery structure after annealing without recrystallization,and the microstructure was fibrous.The spherical ZrO₂ particles were homogeneous distributed in the matrix,and the diameter was mostly concentrated in the range of 5-35nm.After rolling,the deformation of ZrO₂ and Y₂O₃ particles is different.ZrO₂ particles maintain their spherical shape without obvious deformation.Some Y₂O₃ particles are compressed in the normal direction,and cracks appear on both sides of the particles in the rolling direction.The hardness of Y₂O₃particles is low and it is related to the low interface bonding strength between the substrates.（4）After the dispersion-strengthened Pt-20Rh alloys sheet is welded in the tansverse direction,a tensile test is performed in the rolling direction.The results show that with the increase of the content of ZrO₂ particle,the yield strength and tensile strength of Pt-20Rh welded joints increase significantly.Compared with the base metal,the welded joint of each alloys sample almost maintains its yield stress,and its work hardening ability is greatly reduced.（5）TEM and HRTEM and scanning electron microscopy electron backscatter diffraction were used to characterize the microstructure of Pt-20Rh welded joints.It was found that the grains in the fusion zone of the welded joint showed a as-cast structure,and a large number of small-angle grain boundaries were distributed in the grains.Compared with the small number and size of holes of the base metal,the number and size of voids in the weld line increased significantly,and the number and size of the holes would increase with the increase of the content of ZrO₂.The shape of the ZrO₂particles of the welded joint is spherical,and it is still homogeneous distributed,which can explain the internal cause of the almost unchanged yield strength of the alloys before and after welding.（6）The contact angles between Si O₂-Al₂O₃-Ca O-Mg O glass droplets and dispersion-strengthened Pt-20Rh alloys at 1000-1550°C were studied by the sessile drop method.It was found that the trend of contact angles with temperature is divided into three stages:a gentle wave stage,a sharp drop stage,and a high temperature slow drop stage.When the temperature rises above 1350°C,the contact angle slowly decreases with increasing temperature.Two obvious inflection points at the contact angle-temperature curve can be observed for phase transition of the glass.The critical temperature for whether wetting or not between Si O₂-Al₂O₃-Ca O-Mg O glass droplets and PtRh20 alloy is 1246°C.And that between Si O₂-Al₂O₃-Ca O-Mg O glass droplets and ODS-PtRh20 is 1272°C.The differences of wettability of PtRh20 alloy and ODS-PtRh20 alloy are as follows.When the temperature is below 1300°C,PtRh20alloy is more easily wetted by glass melt droplets.When the temperature is over1300°C,ODS-PtRh20 alloy is slightly easier to be wetted.