Two-stage Hall-Petch relationship in Cu with recrystallized structure

Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a two-stage Hall-Petch relationship.There is a critical grain size of 3μm that divides stagesⅠandⅡwhere the Hall-Petch slope k value are quite different.The stageⅡis supposed to be validified down to 100 nm at least by comparing with a Cu-Ag alloy.The critical grain size varies in different materials systems,and the underline mechanisms are discussed based on the dislocation glide modes.

Friction stir based welding and processing technologies-processes,parameters,microstructures and applications:A review

Friction stir welding [FSW） has achieved remarkable success in the joining and processing of aluminium alloys and other softer structural alloys. Conventional FSW, however, has not been entirely successful in the joining, processing and manufacturing of different desired materials essential to meet the sophis- ticated green globe requirements. Through the efforts of improving the process and transferring the existing friction stir knowledge base to other advanced applications, several friction stir based daughter technologies have emerged over the timeline, A few among these technologies are well developed while others are under the process of emergence. Beginning with a broad classification of the scattered fric- tions stir based technologies into two categories, welding and processing, it appears now time to know, compile and review these to enable their rapid access for reference and academia. In this review article, the friction stir based technologies classified under the categol^J of welding are those applied for join- ing of materials while the remnant are labeled as friction stir processing （FSP） technologies. This review article presents an overview of four general aspects of both the developed and the developing friction stir based technologies, their associated process parameters, metallurgical features of their products and their feasibility and application to various materials. The lesser known and emerging technologies have been emphasized.

Microstructure and Mechanical Properties of Dissimilar Double-Side Friction Stir Welds Between Medium-Thick 6061-T6 Aluminum and Pure Copper Plates

It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding.Thus,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed.It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMC)layer is formed at the Al/Cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the joint.With the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface.The maximum tensile strength and elongation of Al/Cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/min.In addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides.The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.

Front-end readout electronics system of ProtoDUNE-SP LAr TPC

Purpose As a prototype of Deep Underground Neutrino Experiment far detector,ProtoDUNE single-phase Liquid Argon(LAr)Time Projection Chamber(TPC)sits in H4 beam line at CERN to characterize detector response.It consists of 6 full-size Anode Plane Assemblies(APAs)plus 18 Cathode Plane Assembly(CPA)modules to form two 3.6-m drift regions with a total of 15,360 readout channels.To achieve a good signal-to-noise ratio with this noble liquid detector(770ton LAr),cold electronics developed at BNL for extremely low temperature(77K–89K)operation is an optimal solution,which decouples the electrode and cryostat design from the readout design.Methods With CMOS front end ASICs integrated with the TPC electrodes,the electronic noise is independent of the fiducial volume and much lower than with readout electronics at room temperature.In addition,signal digitization and multiplexing to high-speed links inside the cryostat result in large reduction in the quantity of cables and the number of cryostat penetrations,giving the designers of both the TPC and the cryostat the freedom to choose the optimum configurations.Results and conclusions By April 2018,we have successfully instrumented 6 APAs with cold electronics,and the results of the integration test before the final installation in the cryostat look very promising.