Influence of Surface Mechanical Attrition Treatment (SMAT) on Microstructure, Tensile and Low-Cycle Fatigue Behavior of Additively Manufactured Stainless Steel 316L
, Tao Wu 1,2,3,*,†, Fei Sun 4, Chong Wang 5, Jian Lu 6 and Thomas Niendorf 1Round 1
Reviewer 1 Report
Reviewer's comments
Manuscript ID: metals-1886535
Title: Influence of surface mechanical attrition treatment (SMAT) on microstructure, tensile and low-cycle fatigue behavior of additively manufactured stainless steel 316L
Authors: Thomas Wegener *, Tao Wu, Fei Sun, Chong Wang, Jian Lu, Thomas Niendorf
In this study, 316L specimens are fabricated by DED and subsequently subjected to SMAT treatment. Both uniaxial tensile tests and uniaxial tension-compression low-cyclic fatigue (LCF) tests were conducted for as-built and SMAT processed specimens. The effects of SMAT treatment on the microstructure, hardness and fatigue properties of the DED 316L sample are investigated. A comparison of the resulting cyclic stress amplitude, half-life hysteresis loops and cyclic hardening/softening was performed for the untreated and SMAT processed specimens. The detailed microstructures of the samples are examined by using Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). The aim of the present paper can be of practical interests and the article is of scientific merit. The results present in this work are impressive and worth of publication after minor revision. Specific comments are given below.
Q1. The description in Line 294 and 295 does not match the results shown in Figure 4.
Q2. Please refer the paper published in Surface Coating and Technology, 344 (2018) 295-302, entitled Insight into formation of gradient nanostructured (GNS) layer and deformation induced martensite in AISI 316 SS subjected to severe shot peening. The lath-like microstructure shown in Fig. 4d and diffraction pattern of deformed layer shows the presence of strain-induced martensite in the deformed layer. In the article, the authors seem ignore the existence of martensite and its effect on strain hardening and the cause of low ductility.
Q3. The layer 1, layer 2 and layer 3, mentioned in Line 276, Line 293 and Line 326 should be marked in Figure 7.
Q4. The fatigue life/strength of shot-peened sample is sensitive to the sample surface roughness. Would the authors provide the surface roughness of the tested samples? The readers may want to know the change in surface roughness after SMAT, increase or decrease in surface roughness relative to the as-built sample.
Q5. Please refer the paper published in Materials 2017, 10, 187; doi:10.3390/ma10020187, entitled Stress corrosion cracking susceptibility of 304L substrate and 308L weld metal exposed to a salt spray. In a conventional fusion weld, the δ ferrite can be formed in the deposit intra- and inter-granularly (Fig. 4 ). In this DED 316 sample, as shown in Fig. 3b, the δ ferrite can be located along the solidified boundaries and within the columnar grains. The authors should confirm the statement about their results in Line 260.
Q6. With determined chemical compositions, the amount of ferrite formed in a stainless steel fusion zone can be estimated by Schaeffler diagram. Such rule may fail because of the low energy input of the DED process. Can the authors give a few statements about the amount of ferrite formed in the DED 316 in comparison with the conventional fusion weld under the same compositions.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript reads well. Here some additional suggestions to further improve the quality of this:
-check the MDPI template one more time. The editorial office will ask you for all email addresses
-only define abbreviations in the abstract if you subsequently use them
-line 55-65: decreasing prices for metal powder also allowed and allows DED to substitute other fabrication processes such as diffusion bonding (https://doi.org/10.3390/met10050613)
-line 126-137: Maybe emphasize one more time the novelty and importance of this work
-maybe provide the european and chinese names for AISI 316L Stainless steel
-Results and experiments are excellent
-Conclusions you can use the abbreviations now since they have been introduced earlier
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
