Investigation On Microstructures And Mechanical Properties Of Components Manufactured By Double Hot-wire And Plasma Arc Additive Manufacturing Processing

The advantages of wire plasma arc additive manufacturing processing are low production cost,high forming precision,and very suitable for the production of large parts.In this paper,the plasma arc additive manufacturing processing is combined with the double-filling process and the hot-wire welding process,a new double hot-wire and plasma arc additive manufacturing(DHW-PAM)processing is proposed.In the test,the high nitrogen austenitic stainless steel(high nitrogen steel)wire and the 308 L stainless steel wire were used as the filler wire,and the hot-wire processing was compared with the cold-wire processing.Finally,the effects of arc traveling speed and wire filling process on the forming efficiency,microstructure and mechanical properties were deeply explored.Firstly,the DHW-PAM system was designed and constructed,including the design of the double hot-wire manufacturing device and the monitoring system of the additive process.On the basis of the original plasma arc material adding manufacturing system,a precise and controllable double hot-wire manufacturing device was constructed.It uses two sets of independently adjustable wire feeders to feed wires,and two constant-current power supply to heat the wires.And the process monitoring system was improved.The hot wire current and voltage monitoring module and the interlayer temperature detection module were added to the current and voltage monitoring system of welding power source.Then the monitoring software and query software were also redesigned.The system can not only meet the requirements of DHW-PAM,but also perform real-time monitoring and process feature discrimination on the additive manufacturing to achieve process specification optimization.Secondly,the comparative test of single cold-wire processing and single hot-wire processing for high nitrogen steel was carried out to explore the technological characteristics of high nitrogen steel single hot-wire processing.With the same process parameters,the forming efficiency of single hot-wire processing is 2.02 times as much as single hot-wire processing.And the mechanical properties test shows the tensile strength of the single hot-wire samples decrease slightly,but still reach 1086 MPa which is 99.6 % of the base metal strength.The result shows that the single hot-wire processing can increase the forming efficiency to more than 2 times while ensuring the tensile strength of the additive sample.Then,the single cold-wire processing and single hot-wire processing was compared with 308 L stainless steel wire filling.It is found that the single hot-wire processing can effectively reduce the wire loss without changing other parameters,and improve the forming efficiency to 2.05 times.The microstructure observation shows that the grain size is refined from 10.41 μm,9.42 μm and 8.37 μm to 9.98 μm,8.71 μm and 7.62 μm by single hot-wire processing.Therefore,single hot-wire processing can significantly improve the forming efficiency of the additive manufacturing and refine the grain size of stainless steel.Finally,the characteristics of stainless steel DHW-PAM processing were deeply explored.Compared with double cold-wire processing,the DHW-PAM processing is more sensitive to the arc traveling speed and has a smaller process range.And the forming efficiency of DHWPAM processing is 3.89 times as much as single hot-wire processing,and 2.10 times as much as double hot-wire processing.The microstructures of the DHW-PAM samples are finer,and the tensile strength and elongation are also slightly higher.In short,the DHW-PAM process can greatly improve the forming efficiency and refine the grain size,while slightly improving the tensile properties of the samples.