The Microstructure and Mechanical Properties of TA1-Low Alloy Steel Composite Plate Manufactured by Explosive Welding
Round 1
Reviewer 1 Report
This paper tells us about «Ti-steel» composites obtained by explosive welding. The authors analyze the microstructure of welds and bonding strength as well as nucleation and propagation of cracks during mechanical loading. The paper is well-written and well-organized; however, the aim of this study is quite questionable. «Ti-steel» explosively welded compositions are known for a long time. There are a great number of research papers on this subject and moreover, this combination has a commercial application. Due to this fact, the authors should clarify in detail, what new they have done and found in their study compared to previous investigations.
Also, I would suggest the following improvements:
- The quality of weld seam strongly depends on the explosive welding regimes. Authors describe some unknown sample at 12 pages and analyze the cracks, vortices and diffusion zones it. But we even don’t know, how this sample was prepared? Which explosive authors chose? What was the detonation speed? Collision point speed? Collision angle? Why authors decided that even this regime was the best? Is it possible to completely exclude negative microstructural factors by varying the regimes?
- In my opinion, the term “high-resolution image” is not correct concerning optical microscopy and SEM images which authors provide in Fig. 3 and 4. It’s better to say a “magnified” image.
- In line 146 authors write that they didn’t find intermetallic by EDS. I guess here they are talking about the interface free of vortices. It’s better to specify, otherwise, it’s a bit confusing. Also, conclusion 6: There is no IMC in the Ti alloy /LAS steel bonding interface. But what about vortices?
- Please, provide the composition of diffusion layers in at. %.
- As intermetallic regions were formed at the interface, it should be seen in the microhardness graph by an increase of HV to at least 600 HV. Or at measurement authors avoided these zones?
- There are some typos and grammar mistakes through the manuscript, e.g.:
Line 157: at the of
Line 237: propagate -> propagates.
Also revise the articles, e.g. line 243: explosive welded TA1/LAS steel composite plate -> the explosive welded TA1/LAS steel composite.
Please, read carefully and fix the mistakes.
Author Response
Response to Reviewer 1 Comments
This paper tells us about «Ti-steel» composites obtained by explosive welding. The authors analyze the microstructure of welds and bonding strength as well as nucleation and propagation of cracks during mechanical loading. The paper is well-written and well-organized; however, the aim of this study is quite questionable. «Ti-steel» explosively welded compositions are known for a long time. There are a great number of research papers on this subject and moreover, this combination has a commercial application. Due to this fact, the authors should clarify in detail, what new they have done and found in their study compared to previous investigations.
Also, I would suggest the following improvements:
Point 1: The quality of weld seam strongly depends on the explosive welding regimes. Authors describe some unknown sample at 12 pages and analyze the cracks, vortices and diffusion zones it. But we even don’t know, how this sample was prepared? Which explosive authors chose? What was the detonation speed? Collision point speed? Collision angle? Why authors decided that even this regime was the best? Is it possible to completely exclude negative microstructural factors by varying the regimes?
Response 1: Thank you for your kind advice. The explosive welding condition was added as “In the present work, composite plate was explosively welded by using expanded ammonium nitrate as explosive material, and detonation velocity was 2.1 km/s.” (Line 99) The objective of the this work is to analyze the effect of bonding interface microstructure on the mechanical properties and crack propagation of Ti/steel composite plate, rather than to obtain the best microstructure by controlling the explosive welding regimes. Therefore, the explosive welding regimes and their effect of explosive welding regimes were not studied. The authors did not obtain samples without negative microstructures by varying the regimes, now.
Point 2: In my opinion, the term “high-resolution image” is not correct concerning optical microscopy and SEM images which authors provide in Fig. 3 and 4. It’s better to say a “magnified” image.
Response 2: Thanks very much for your kind advices, the “high-resolution image” was replaced by the term “magnified image”, now. (Line 143 and 157)
Point 3: In line 146 authors write that they didn’t find intermetallic by EDS. I guess here they are talking about the interface free of vortices. It’s better to specify, otherwise, it’s a bit confusing. Also, conclusion 6: There is no IMC in the Ti alloy /LAS steel bonding interface. But what about vortices?
Response 3: Thanks very much for your kind advices, we specify these region are free of vortices as “Typical interface microstructure and compositional profiles of Ti/steel interface without vortices in different regions are shown in Figure 6. It is evident that EDS did not show any traces of IMCs in Ti/steel interface free of vortices.”(Line 171)
Point 4: Please, provide the composition of diffusion layers in at. %.
Response 4:The line scanning of EDS were shown in Figure 6(b) and 6(c). And the results show that the composition of Ti concentration decreases from the TA1 side (near 100%) to the LAS side (near 0) and there are no Ti concentration platform appears, which suggest that no IMCs formed in diffusion layers. Therefore, there is no a typical composition of diffusion layers.
Point 5: As intermetallic regions were formed at the interface, it should be seen in the microhardness graph by an increase of HV to at least 600 HV. Or at measurement authors avoided these zones?
Response 5: In this paper, an important feature is the IMCs only appear in the vortex regions and these vortex regions are always enclosed by steel regions, which make the IMCs regions are discontinued. Since the width of the vortex zone is only about 100μm, and the width of TA1 / LAS interface wavy is about 1000μm. Therefore, only 10% of the test results will be affected by the high hardness IMC near the interface, when positions were chosen randomly for hardness testing. Therefore, the microhardness diagram of the explosion welding will not show the high hardness peak caused by the IMC layer.
In this paper, we chose the position of microhardness, randomly. The results suggest that there is no hardness peak caused by IMC, and fine grain strengthening effect is the main effect factor of microhardness. Similar result was also shown in Figure 7 of “Interface Characteristic of Explosive-Welded and Hot-Rolled TA1 / X65 Bimetallic Plate ”(Metals 2018, 8, 159; doi: 10.3390 / met8030159). In their work, discontinued IMCs were also formed at interface, and the hardness near interface was lower than 200HV.
Point 6: There are some typos and grammar mistakes through the manuscript, e.g.:
Line 157: at the of
Line 237: propagate -> propagates.
Also revise the articles, e.g. line 243: explosive welded TA1/LAS steel composite plate -> the explosive welded TA1/LAS steel composite.
Please, read carefully and fix the mistakes.
Response 6: Thanks very much for your kind advices, we fixed these mistakes, now.
- The “at the of” was replaced by “at the trough of” at Line183.
- The “the micro-crack initiated at crest regions need to propagate a long distance to connect” was replaced by “the micro-cracks initiated at crest regions need to propagate a long distance to connect” at Line 265.
- The “explosive welded TA1/LAS steel composite” was replaced by “the explosive welded TA1/LAS composite” at Line 273.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper deals with the characterization of Ti/Steel clad made by explosive welding and is considered authors' own work but is weak in the following aspects.
- Explosive welding condition is not well demonstrated. Since it is a case study under one experimental condition, the condition should be demonstrated clearly. Also, so many works have been made on explosively welded Ti/Steel clads, the progress in the present investigation should be demonstrated. (mandatory)
- Fig.11; The authors reported "kink" in steel close to the interface, but it is not clear for the reviewer on the definition. Kink is normally formed in HCP such as Zn and Mg.
- References should be checked again.
Author Response
Response to Reviewer 2 Comments
The paper deals with the characterization of Ti/Steel clad made by explosive welding and is considered authors' own work but is weak in the following aspects.
Point 1: Explosive welding condition is not well demonstrated. Since it is a case study under one experimental condition, the condition should be demonstrated clearly. Also, so many works have been made on explosively welded Ti/Steel clads, the progress in the present investigation should be demonstrated. (mandatory)
Response 1: Thank you for your kind advice. The explosive welding condition was added as “In the present work, composite plate was explosively welded by using expanded ammonium nitrate as explosive material, and detonation velocity was 2.1 km/s.” (Line 99)
And the introduction was rewritten to demonstrate the progress of explosively welded Ti/steel composition as:(Line 34-94)
The production of a composite plate with Ti alloys and steels requires a reliable bonding interface between these dissimilar alloys. Different welding techniques have been used to produce Ti/steel composite plates. For example, Balasubramanian produced Ti/steel joints by diffusion welding. He found various intermetallic compounds (IMCs) formed in the diffusion zone, weakening the mechanical properties of the Ti/steel joints. Chen et al. produced Ti/steel joints with laser butt welding and found that the fractures are brittle for various IMCs formed along the interface. Yu et al. prepared Ti/steel composite plates with hot-roll bonding, determining that the interface is ductile when the formation of IMCs is inhibited. Miriyev et al. used a spark plasma sintering technique to join Ti to steel, and found that a titanium carbide layer formed at the bonding interface could prevent the formation of IMCs. These results suggested that the preparation of high quality Ti alloy/steel composite plates is very difficult, mainly due to brittle IMCs are always formed at the bonding interface through atom diffusion. Miriyev et al. suggested these IMCs significantly reduce the mechanical properties of the composite plate. Moreover, Ti and steel exhibit significant differences in their chemical and physical properties, and titanium alloy easily absorbs nitrogen and oxygen, making it difficult to avoid bonding defects. These problems make conventional welding unsuitable for producing Ti/steel composite plates.
Researchers reviewed explosive welding as a widely used technique in the manufacture of composite plates. It is well known that explosive welding can directly weld similar metals and dissimilar metals that are not easily welded by other techniques. The composite plates prepared by explosive welding usually have a wavy metallurgical interface. The wavy bonding interface is caused by the pressure impulses when the plates collide. Moreover, the metallurgical bonding interface does not cause significant crystallization and phase transformation. As such, Bataev et al. showed that explosively welded plates can have higher mechanical properties than bulk plates with similar chemical compositions. Therefore, explosive welding has been used since its invention to design and control the microstructure of the interfaces of dissimilar materials and enforce their mechanical properties.
Explosive welding is well suited for the control of the microstructures of Ti/steel interfaces to improve interfacial strength and offers a great potential for the high-quality welding of Ti and steel. So far, many scholars have researched the interface structure of Ti/steel explosive welded composite plates. Nishida et al. found metastable phases produced at the bonding interfaces of the Ti/steel joints to be inevitable during the melting of the bonding interface. Xie et al. also found brittle Fe diffusion zones, formed near the bonding interface of CP-Ti/X65 composite plates, produced by explosive welding and hot rolling. Song et al. found that four successive hierarchical structures are formed at the interface of the explosively welded Ti/steel cladding joint. Metastable Fe9.64Ti0.36 and FeTi are formed near the crest region, and these inclusions are always accompanied by similar dimension microcracks. Yang et al. found that very fine grains are produced in the adiabatic shear band in the Ti/steel explosive welded bonding interface, which suggest a recrystallization process took place during the explosion. Kahraman et al. found that brittle IMCs lead to a decrease in the mechanical properties of Ti/steel joints, and the reduction of brittle IMCs is a key step for improving the mechanical properties. However, the relationship between the interface structure produced by explosive welding and its influence on the mechanical properties and crack propagation in Ti/steel composite plates has not been studied systematically.
IMCs are a key factor in controlling the mechanical properties of the Fe/Ti interface. In addition, the ductile phase has an important influence on the performance of the weld. Chu et al. found that crack nucleation and propagation in Ti/Fe composite plates were affect by the structures of the IMC and ductile phases. Therefore, it is worth investigating the effect of the complex bonding interface produced by explosive welding on the mechanical properties and crack propagation of dissimilar Ti/steel composite plates.
The purpose of this work is to analyze the effect of the bonding interface microstructure on the mechanical properties and crack propagation of dissimilar Ti/steel composite plates. TA1 Ti alloys and low carbon steel (LAS) composite plates were produced by explosive welding. Their microstructure was analyzed using optical microscopy (OM), scanning electron microscopy (SEM) and energy spectrum analysis (EDS). Furthermore, their mechanical properties were studied using microhardness, tensile, shear and bend testing.
Point 2: Fig.11; The authors reported "kink" in steel close to the interface, but it is not clear for the reviewer on the definition. Kink is normally formed in HCP such as Zn and Mg.
Response 2: Thank you for your kind suggestion. These "kink" are a kind of large angle bending at the bonding interface, which are not the kinks always formed in HCP. And the description about these interface kink is modified as “It is seen that there are some large angle bending at the bonding interface, which was signed as kinks (at positions 1, 2 and 3). Because the diffusion layer is very thin, these interface kinks caused the steel matrix to appear in front of micro-crack tips and promoted crack blunting, plastic energy dissipation before the micro-crack tips and propagated to the steel matrix as indicated by yellow arrow.” (Line 246)
Point 3: References should be checked again.
Response 3: The references were rechecked base on the new introduction, now. And the DOIs were deleted, now.
Author Response File: Author Response.pdf
Reviewer 3 Report
In the article, the authors described the structure and properties of the TA1 Ti and low carbon steel explosive welding joint. Interesting job, but at a basic level. The description of welding technology is missing in the paper, which makes it impossible to analyze of the impact of process parameters on structure and properties. Another problem is a lack of phase identification in the connection area. The description of the joint structure is incomplete and needs to be completed.
The work can be published after completing the description of the joining technology and a full description of the structure, not only on the basis of light microscopy and scanning electron microscopy but also for example by means of transmission microscope.
Author Response
Response to Reviewer 3 Comments
In the article, the authors described the structure and properties of the TA1 Ti and low carbon steel explosive welding joint. Interesting job, but at a basic level. The description of welding technology is missing in the paper, which makes it impossible to analyze of the impact of process parameters on structure and properties. Another problem is a lack of phase identification in the connection area. The description of the joint structure is incomplete and needs to be completed.
The work can be published after completing the description of the joining technology and a full description of the structure, not only on the basis of light microscopy and scanning electron microscopy but also for example by means of transmission microscope.
Point 1: The work can be published after completing the description of the joining technology and a full description of the structure, not only on the basis of light microscopy and scanning electron microscopy but also for example by means of transmission microscope.
Response 1: Thank you for your kind advice. The explosive welding condition was added as “In the present work, composite plate was explosively welded by using expanded ammonium nitrate as explosive material, and detonation velocity was 2.1 km/s.” (Line 99)
The main objective of the this work is to analyze the effect of bonding interface microstructure on the mechanical properties and crack propagation of dissimilar Ti/steel composite plates.
The main factors that inhibit crack propagation are the distribution of brittle region (IMC in this paper) and plastic region (the fine-grain steel in this paper) at the interface. It has been explained by OM and SEM. The structure change of the IMCs due to the alloy composition could not affect the mechanical properties of these brittle phase, obviously. And there is no new phases are formed in the diffusion layer as shown in figure 6. Therefore, authors think that analyzing the phase composition by TEM can not provided more information about the objective of the this work.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Now the aim of this work is more clear and the motivation coincides with the methods chosen and conclusions drawn. Please pay attention that you wrote the aim twice (lines 77 and 88), I think it's excess.
Also, the authors write "However, the relationship between the interface structure produced by explosive welding and its influence on the mechanical properties and crack propagation in Ti/steel composite plates has not been studied systematically". I can't say that this study investigates this relationship systematically. The authors only present one special case, and I can't imagine how this study can have "guiding significance for the design of bonding microstructures to obtain excellent mechanical properties of explosively welded Ti/steel composite plates".
Author Response
Point 1: Now the aim of this work is more clear and the motivation coincides with the methods chosen and conclusions drawn. Please pay attention that you wrote the aim twice (lines 77 and 88), I think it's excess.
Response 1: Thank you for your kind advice. The second purpose of this work was deleted. (Line 88)
Point 2:Also, the authors write "However, the relationship between the interface structure produced by explosive welding and its influence on the mechanical properties and crack propagation in Ti/steel composite plates has not been studied systematically". I can't say that this study investigates this relationship systematically. The authors only present one special case, and I can't imagine how this study can have "guiding significance for the design of bonding microstructures to obtain excellent mechanical properties of explosively welded Ti/steel composite plates".
Response 2: Thank you for your kind advice. “systematically” is deleted.(line 75) And the “would certainly have a guiding significance” is replaced by “make a step ”(line 79)
Reviewer 2 Report
The paper still includes doubts written as follows.
Line 97; “low carbon steel” seems “low alloy steel”.
Line 98-100; The experimental condition of explosive welding should be demonstrated more in details. Thickness, density of explosive and the gap between plates. (mandatory)
Line 246 and later; The author reported “kinks”, but these are not suggested by other figures in the manuscript. Also, the reviewer has never seen such deformed region in explosively welded interface in journal papers. Reliable citation is requested as to accept the paper. (mandatory)
Author Response
Point 1: Line 97; “low carbon steel” seems “low alloy steel”.
Response 1: Thank you for your suggestion. The “low carbon steel” was replaced by “low alloy steel”.(line 88)
Point 2: Line 98-100; The experimental condition of explosive welding should be demonstrated more in details. Thickness, density of explosive and the gap between plates. (mandatory)
Response 2: Thank you for your suggestion. The experimental condition of explosive welding was added as “In the present work, composite plate was explosively welded by using expanded ammonium nitrate as explosive material. The thickness of explosive is 30 mm and the density is 0.6g/cm3. The stand off distance is 6 mm and detonation velocity was 2.1 km/s.”(line 96)
Point 3:Line 246 and later; The author reported “kinks”, but these are not suggested by other figures in the manuscript. Also, the reviewer has never seen such deformed region in explosively welded interface in journal papers. Reliable citation is requested as to accept the paper. (mandatory)
Response 3: Thank you for your suggestion. Several similar interface kinks were shown in other papers: for example, figure 2b of “Experimental and numerical investigation of microstructure and mechanical behavior of titanium/steel interfaces prepared by explosive welding”(Materials Science & Engineering A 689 (2017) 323–331) and Figure 9a of “Microstructure and property inhomogeneity investigations of bonded Zr/Ti/steel trimetallic sheet fabricated by explosive welding” (Journal of Alloys and Compounds 698 (2017) 835-851). These figures suggest that the interface kinks are common structure formed in Ti/Fe explosive welded composite.
The citation was added as “Similar interface structure were also found in other Ti/steel explosive welded composites [31,34]”(line 245)
Author Response File: Author Response.pdf
Reviewer 3 Report
Slight corrections that do not describe the technological procedure of joining, no clear identification of the phases in the structure,
but in general the article constitutes a whole, brings elements of knowledge to materials science and mechanical engineering and can be published
Author Response
Point 1:Slight corrections that do not describe the technological procedure of joining, no clear identification of the phases in the structure, but in general the article constitutes a whole, brings elements of knowledge to materials science and mechanical engineering and can be published.
Response 1: Thank you for your suggestion. More technological procedure of joining added as “In the present work, composite plate was explosively welded by using expanded ammonium nitrate as explosive material. The thickness of explosive is 30 mm and the density is 0.6g/cm3. The stand off distance is 6 mm and detonation velocity was 2.1 km/s.” (line 96)
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
Nothing special.
