Micro-Brazing of Stainless Steel Using Ni-P Alloy Plating
, Ikuo Shohji 1, Makoto Iioka 2, Anna Hashimoto 2, Junichiro Hirohashi 3, Tsunehito Wake 3 and Susumu Arai 4Round 1
Reviewer 1 Report
Electroplating can be used to produce Ni-P coating layer for decades, so as the application of Ni-P alloy for brazing filler of hard-to-wet materials, such as graphite, ceramics etc,. This work combined the electroplating and brazing of Ni-P alloy for joining of stainless steel. The experiment design, procedure and result are clear. Some issues should be addressed to make this article scientifically meaningful.
For a thin-well component as mentioned by authors, how suitable it is to braze it with Ni-P alloy of the eutectic point at 890oC? Does such a high brazing temperature result in concentration of residual thermal stress? I asked this question because the shear strength of brazed joints is of 43MPa, which is much lower than other filler alloy and Ni-P alloy.
Should author have make some discussion on the experimental result. For instance, what the interface Fe-Cr-Ni phase is and any information available in in Fe-Ni or Ni-Cr phase diagrams?
"These phases are brittle compounds and thus they seems to reduce the strength of the brazed joints." in line 150-151. The author has readily obtained the microstructure of Ni-P brazing zone in Fig.6 a, and why not discuss a little bit on this?
Fig.7 and 8 could be combined; Table 3 is not necessarily given; Fig.6 the color of EPMA mapping is not reader friendly; some language issue exists. Brazing filler metal (BFM) is not a well accepted expression, one could just use " filler alloy" or "Filler metal".
Author Response
Response to Reviewer 1’s Comments
Dear Reviewer:
I am very grateful to your comments for the manuscript. Based on your comments and requests, we have made extensive modification on the original manuscript. Also, we carefully proof-read the manuscript to minimize typographical, grammatical, and bibliographical errors. Here below is our description on revision according to your comments and requests.
Point 1:
For a thin-well component as mentioned by authors, how suitable it is to braze it with Ni-P alloy of the eutectic point at 890 °C? Does such a high brazing temperature result in concentration of residual thermal stress?
Response 1:
In industrial production, the nickel base filler alloys are commonly used for brazing stainless steel due to their good corrosion resistance, high hardness and other properties. Since the nickel base filler metal itself, e.g. BNi-5, is inherently high melting temperature (around 1100-1200 °C), its brazing temperature is higher. Therefore, it is considered that there is no problem in practical use.
On the other hand, for lowering the melting temperature of nickel filler metal, P as the melting point depressant has been often contained in the nickel. The eutectic Ni-11P filler alloy (code number BNi-6 (JIS Z 3265)) has been often used in brazing stainless steel, especially for the thin-walled components, due to its lowest melting temperature, extremely good fluidity and excellent brazability. Furthermore, the lower melting temperature of the filler metal makes it easy to set the brazing temperature when to conduct the brazing. We have already discussed this issue in the revised manuscript (ref. to the Introduction).
Point 2:
What the interface Fe-Cr-Ni phase is and any information available in in Fe-Ni or Ni-Cr phase diagrams? "These phases are brittle compounds and thus they seems to reduce the strength of the brazed joints." in line 150-151. The author has readily obtained the microstructure of Ni-P brazing zone in Fig.6 a, and why not discuss a little bit on this?
Response 2:
According to the Fe-Ni-Cr ternary phase diagraph (ref. to the line 173 in the revised manuscript), the bright gray phase (A) is identified to be the (Fe, Ni, Cr) solid solution.
We modified the discussion of the microstructure of the brazed joint. Please refer to the lines 181-186 (highlighted in blue), 195-197 (highlighted in green).
Point 3:
Fig.7 and 8 could be combined
Response 3:
We have combined the Figure 7 and 8. Please refer to the line 210 (highlight in green) in the revised manuscript.
Point 4:
Table 3 is not necessarily given
Response 4:
The table 3 was removed from the revised manuscript, and we presented the shear strength byword in the text (ref. to the lines 218-219).
Point 5:
Fig.6 the color of EPMA mapping is not reader friendly
Response 5:
The color bar presented in Figure 6 seems to be not read friendly, we attached a ``Detected Count‘’ near the bar so that make it to be read friendly. Please refer to the line 169 (highlight in green) in the revised manuscript.
Point 6:
Brazing filler metal (BFM) is not a well accepted expression, one could just use " filler alloy" or "Filler metal".
Response 6:
We have changed all the ``BFM’’ to ``filler metal’’ in the revised manuscript. Please refer to the lines 19, 24, 26, 78, 174(highlight in green).
In addition, in order to make this article scientifically meaningful, we did a major revised in the original manuscript. Below is our revised in Introduction, Experimental procedure, Results and discussion:
⑴ We improved the background of our study. Please refer to the lines 31-45 (highlight in blue) and lines 46-74 (highlight in yellow) in the revised manuscript.
⑵ We added all the device models and experimental set-up to the revised manuscript so that make this study more scientifically. Please refer to the lines 99-105, 112-114 (highlight in yellow).
⑶ The XRD spectrum was wrong. We showed the result of XRF in the figure. The XRD graph and the discussion of the XRD analysis were revised in the manuscript, please refer to the lines 136-140 and 151, which were highlighted in yellow.
We modified the discussion of XRD analysis result. Please refer to the lines 136-140 (highlight in yellow).
⑷ The discussion of the shear test was improved. Please refer to the lines 211-218 (highlight in yellow).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper addresses the subject of stainless steel brazing using an electroplated Ni-11 %wt. P layer as a brazing filler metal. The electroplating method is positioned as more reliable and more repeatable for industrial use, particularly, in a case of complicated shapes. This affirmation is not so clear, since electrodeposition onto complicated shapes is not as uniform, as, for example, electroless deposition. From the introduction is also not so clear the choice of Ni-11P composition as one of the authors main interest.
The Experimental procedure is not described in an appropriate way. All the analysing techniques are just mentioned, the device models and experimental set-up should be described clearly (XRF, XRD, SEM, EPMA, OM). For example, the XRD spectrum presented in the paper in Figure 4, has no background. In which configuration it has been acquired, on which area it has been analysed, is the background subtracted?
The resolution of the figures 1 and 2 is deteriorating the quality of the paper. I suggest to improve it.
The English should be improved, particularly, the use of articles and the use of different tens in the text.
Below you can find the point by point comments to different lines of the manuscript:
16, 25, 45 (mass %) wt. % is more common
21 is mainly concentrated
22 the average shear strength
24 compelted realized
32 commercial brazing filler metal (if it is commercial, the ref. should be completed with the trademarks and names)
33 lightweighting
35 the proper
36 brazed area. An inappropriate quantity of BFN caused degradation and decreases reliability..
41 lend lead
55 as the stirrer for stirring /bubbling/mixing
59 new paragraph
62, 81, 84 Plateding layer
68 cross-sectional
75 Figure 1: “temperature contrioller” “power supplyer”. A limited plated area is shown but is not described how.
78 Figure 2: The figure, in general, is not clear: it consists of 2 schemes. If the first scheme is representing brazed pieces’ geometry, the second one, if it is the magnification of the first one, does not correspond to the first one. Maybe is a new scheme of a new type of samples for the analysis, but, unfortunately, is not so clear from the text.
I suggest indicating the units (mm or um) near the number they are referring to and not below the picture.
81 Plateding layer
83, 92 in a bath
86 is a chemical reaction
92 to modify the sentence
96 intense
97 exists
99 since the XRD-spectrum background is subtracted with unknown protocol, there is no any guarantee that the layer is crystalline since possible amorphous part could be removed by forced background subtraction
106 increases
106-115 Is the time of deposition the same, is the thickness of the layer the same? The information is limited
111 resulted in a
118 elements are homogeneously distributed
120 were formed
121 the component
121 the chemical composition
122 was analysed
123 main components composition
123 small amounts
124 Moreover… the sense of the sentence is not clear
127 are highly concentrated
129-130 to modify the sentences
132 on them
132 Why do you consider the phase Fe-Ni-Cr is you detect much lower content of Cr?
133 P was mainly
137 Table 2: Precision of the % shown in the table has no physical sense
142 The results on shear strength must be commented somehow: is it a good result? It seems low. Compare, please, with the other data in the literature. Maybe you can use the table 3 to express it.
145 Table 3 has no sense as it is presented the same data you have described byword in the text already. If you show the result of each of the 4 measurements it has more sense.
146 result is shown
151 seems
151 The information provided by figure 7 is not clear. Probably, is missing the SS part in order to see where is the fracture.
151 On figure 8 I suggest highlighting the cracks, that, I guess, the authors wanted to show.
158 under the following conditions: ..the current density.. the plating time
161 to modify the sentence
Author Response
Response to Reviewer 2’s Comments
Dear Reviewer:
I am very grateful to your comments for the manuscript. Based on your comments and requests, we have made extensive modification on the original manuscript. Also, we carefully proof-read the manuscript to minimize typographical, grammatical, and bibliographical errors. Here below is our description on revision according to your comments and requests.
Point 1:
The paper addresses the subject of stainless steel brazing using an electroplated Ni-11 %wt. P layer as a brazing filler metal. The electroplating method is positioned as more reliable and more repeatable for industrial use, particularly, in a case of complicated shapes. This affirmation is not so clear, since electrodeposition onto complicated shapes is not as uniform, as, for example, electroless deposition.
Response 1:
We agree with your point of view that the electroless deposition can form a more uniform coating onto complicated shapes than the electrodeposition. But, our study is for the brazing of plate-fin heat exchangers, the shape of the stainless steel components are thin-walled plate. Furthermore, the object plated film is as thinner as 20 μm. Therefore, in this case, we don’t pay much attention to the effect of the coating uniformity, but pay more attention to the deposition rate. Of course, we have conducted a comprehensive comparison of the two methods, and selected the electrodeposition methods in terms of cost reduction and production improvement.
Point 2:
From the introduction is also not so clear the choice of Ni-11P composition as one of the authors’ main interest.
Response 2:
Currently, the eutectic Ni-11P alloy, code name BNi-6 (JIS Z 3265), has been commercially used as the filler metal in foil or paste form because of its lowest melting temperature, extremely good fluidity, especially good for brazing the thin base metal. Furthermore, due to the lowest melting temperature of the Ni-11P filler alloy, it is easy to set the brazing temperature with a hydrogen reduction furnace. At the same time, a lower brazing temperature can reduce power consumption during production. For these reasons, we chose the Ni-11P alloy as the filler metal to conduct the brazing of the stainless steel plates. We have already discussed this issue in the revised manuscript (ref. to the Introduction).
Point 3:
The Experimental procedure is not described in an appropriate way. All the analysing techniques are just mentioned, the device models and experimental set-up should be described clearly (XRF, XRD, SEM, EPMA, OM).
Response 3:
We have added the model, maker and experimental set-up in the revised manuscript. Please check in the revised manuscript (ref. to the lines 99-XRF, 101-XRD, 104-FE-SEM and 112-EPMA, which were highlighted in yellow).
Point 4:
The XRD spectrum presented in the paper in Figure 4, has no background. In which configuration it has been acquired, on which area it has been analysed, is the background subtracted?
Response 4:
The XRD spectrum was wrong. We showed the result of XRF in the figure. Thank you for your comment.
The XRD graph and the discussion of the XRD analysis were revised in the manuscript, please refer to the lines 136-140 and 151, which were highlighted in yellow.
Point 5:
The resolution of the figures 1 and 2 is deteriorating the quality of the paper. I suggest to improve it.
Response 5:
Thank you for your suggestion. We have recreated the figure 1, 2, and have replaced them in the original manuscript (ref. to the lines 93, 97 in the revised manuscript).
Point 6:
The English should be improved, particularly, the use of articles and the use of different tens in the text.
Response 6:
Below is our revision (point by point to different lines of revised manuscript, which were highlighted in yellow, red fonts are the modified parts):
16, 26, 49, 77, 132, 230 mass % →wt.%
22 P mainly concentrated →P is mainly concentrated
22, 206 average of shear strength →average shear strength
25 successfully completed →completely realized
49 commercial brazing filler metal (if it is commercial, the ref. should be completed with the trademarks and names) →code name BNi-6 (JIS Z 3265)
55 lightweighting →lightweigh
60 proper →the proper
60-61 brazed area and inappropriate quantity of it causes degradation of the reliability of the brazed joint. →brazed area. An inappropriate quantity of filler metal caused degradation and decreases reliability of the brazed joint.
66 lend →lead
87 as the stirrer →for stirring
98 new paragraph
103, 121, 123, 124, 128, 130, 131, 135, 147, 151, 152, 153, 157, 159, 160,163, 165,226
plating layer →plated layer
110 cross sectional →cross-sectional
92 temperature controller → temperature controller; power supplyer →power supply
A limited plated area is shown but is not described how. → We added a schematic illustration of the SUS304 plate in the Figure 1, the plate was masked by insulated rubber tape with an exposed surface area of 10 cm2 (3×3.3 cm2).
96 Figure 2: The figure, in general, is not clear: it consists of 2 schemes. If the first scheme is representing brazed pieces’ geometry, the second one, if it is the magnification of the first one, does not correspond to the first one. →We have modified the Figure 2. What we want to present is a front view and a top view of the brazed joint. May be the original figure is not suitable, we are sorry to cause you trouble.
I suggest indicating the units (mm or um) near the number they are referring to and not below the picture. →We have indicated the units near the number they are referring to (shown in Figure 2).
123, 126, 133 in bath →in a bath
126 is chemical reaction →is a chemical reaction
132 to modify the sentence →the Ni-P plated layer, which contains 11 wt.% P and is 20 μm, can be obtained when the H3PO3 in a bath solution is approximately 0.4 M under the plating conditions of the current density of 2.0 A/dm2 and the plating time of 90 min.
154 increases →increase
165-167 Is the time of deposition the same, is the thickness of the layer the same? The information is limited →We have added the plating time and thickness of each plated layer into the revised manuscript. Please refer to the lines 165-167. a) plating time: 180 min, thickness: 18 μm; b) plating time: 90 min, thickness: 15 μm; c) plating time: 40 min, thickness: 16 μm.
160 resulted a loose plated layer →resulted in a loose plated layer
174 elements homogeneously distribute →elements are homogeneously distributed
177 formed →were formed; component →the component
178 Chemical composition →The chemical composition; were analyzed →was analysed
180 main composition →main components; a small amounts of →a small amount of
180-197 Moreover… the sense of the sentence is not clear →We modified this sentence.
196 is highly concentrated →are highly concentrated
191-192 to modify the sentences →There are two kinds of phases in the brazed joint, the dark gray phases and the bright gray phases.
194 to take the chemical composition analysis on them. →to take the chemical composition analysis.
Point 7:
Why do you consider the phase Fe-Ni-Cr is you detect much lower content of Cr?
Response 7:
According to the Fe-Ni-Cr ternary phase diagraph, the bright gray phase (A) is identified to be the (Fe, Ni, Cr) solid solution.
We modified the discussion of the microstructure of the brazed joint. Please refer to the lines 181-186 (highlighted in blue).
199 P mainly concentrated →P was mainly concentrated
171 Table 2: Precision of the % shown in the table has no physical sense →41.3 (Ni),2.0 (P),48.1 (Fe), 8.6 (Cr)
Point 8:
The results on shear strength must be commented somehow: is it a good result? It seems low. Compare, please, with the other data in the literature.
Response 8:
We have made some corrections and additions about the shear test in the revised manuscript (ref. to the lines 211-218, which were highlighted in yellow).
Point 9:
Table 3 has no sense as it is presented the same data you have described byword in the text already. If you show the result of each of the 4 measurements it has more sense.
Response 9:
We removed the Table 3, and presented the shear strength byword in the text (ref. to the lines 204-207).
219 The result shown in Figure 7. →The result is shown in Figure 8(a).
224 thus they seems to →thus they seem to
Point 10:
The information provided by figure 7 is not clear. Probably, is missing the SS part in order to see where is the fracture. On figure 8 I suggest highlighting the cracks, that, I guess, the authors wanted to show.
Response 10:
We modified the SEM image. Please refer to the line 208 Figure 8(a).
Also, we highlighted the cracks so that it can be able to see the location where the failure occurred (ref. to the line 208 Figure 8(b)).
231-232 under the following conditions: ..the current density.. the plating time →under the following conditions: 0.4 MH3PO3 in the bath, the current density of 2.0 A/dm2 and the plating time of 90 min.
234 to modify the sentence →The fracture occurred in the brazed filler zone, where the brittle P-containing compounds exist.
In addition, in order to make this article scientifically meaningful, we improved the introduction. Please refer to the lines 31-74, which were highlighted in blue and yellow.
The discussion of microstructure of the brazed joint was improved in the revised manuscript, which were highlighted in green and blue.
Round 2
Reviewer 1 Report
The author address the issues properly.
Author Response
Response to Reviewer 1’s Comments
Dear reviewer:
I am very grateful to your comments for the manuscript. In order to improve the readability of the manuscript, our manuscript made a language revision by a native speaker.
Reviewer 2 Report
The paper has been improved with respect to the previous version. The figures are more clear. The Experimental procedures have been described in a more detailed way.
The reviewer would strongly suggest careful correction of the grammatical mistakes and improvement of the style. As it was already suggested, it must be controlled the use of articles, commas and the use of different tens in the text. It is possible to guess, that the authors are not native English speakers, but extensive editing is necessary to make your audience understanding the information you bring.
Here the authors can find some additional point by point comments:
25. was completely realized - was successfully realized
32.” corrosion resistance and other properties” sounds strange. Either leave only “corrosion resistance” or add what was really important for your case.
35 “eutectic organization” or “eutectic”. Article is missing
36, 45. thin a low thickness otherwise thin components
37. a larger amount
44. Error in reference?
46-47 the sentence is not clear. Probably, commas are misplaced.
55-56 control, please “multilayer” or “multi-layer”, “plate fin” or “plate-fin”
57-58 change the structure of the sentence
58 “in general” – usually
59 because… hardness and brittleness? modify the sentence
It was already suggested to the authors to change this sentence in order to avoid errors in English, however, it has not been changed..
61. of a/the filler metal
61 correct the tense used
66-67 less costly or more economically favourable
98. Figure 2 is already more clear than before, however, it seems that the authors have provided the side view and the bottom view of the joint (upper should stay better).
102. RINT 2200 VF – is it the model of the XRD machine or the software?
111. cutter
132 It has the sense to clarify here that the chemical composition data from XRF are presented as a plot
138. What does it mean “as-electroplated”? It has a sense if after the authors discuss, for example, some post-treated layers. But is not true
154-161. The effect of the current density and deposition rate is described here, but the conclusion is not clear.
163. And, finally, which recipe was used for the deposition of Ni-11P layers for brazing experiments? The conditions were found in the Conclusions chapter. The reviewer suggests clarifying those conditions also in chapter 3.3.
187 either “a solid solution” or “Fe-Ni-Cr solid solution”
217-218 to modify the sentence
220. suitable for what? How did the authors define that is suitable? Is there any declared limitation on the application of interest?
Probably, it is easier to modify the expression.
Author Response
Response to Reviewer 2’s Comments
Dear reviewer:
I am very grateful to your comments for the manuscript. Based on your comments and requests, we have made modification on the original manuscript. Also, in order to improve the readability of the manuscript, our manuscript made a language revision by a native speaker. Here below is our description on revision according to your comments and requests.
Point 1
The English should be improved, particularly, the use of articles and the use of different tens in the text.
Response 1:
Below is our revision (point by point to different lines of revised manuscript, which were highlighted in gray, red fonts are the modified parts):
25. was completely realized →was successfully realized
32. `` corrosion resistance and other properties” sounds strange. Either leave only “corrosion resistance” or add what was really important for your case. →corrosion resistance and oxidation resistance
35. “eutectic organization” or “eutectic”. Article is missing → a eutectic structure
36, 44. thin thickness →a small thickness
37. large amount →large amounts
43. Error in reference? →[3]
45-46. For a Ni-P alloy, some melting will occur at the lowest melting point (875 °C) of the Ni-P system, regardless of the phosphorus content, provided it is greater than 0.2%.
54. multi-layer plate fin heat exchanger →multilayer plate fin heat exchanger
56-57. change the structure of the sentence →Therefore, a filler metal with a thickness of around 20 μm is required to join the stainless steel.
57. In general →Usually
58-59. because… hardness and brittleness? Modify the sentence →BNi-6 filler metal is formed as a foil or paste because of its inherent hardness and brittleness, making it difficult to supply the correct quantity of the filler metal to the brazed area.
60. of the filler metal
60-61. correct the tense used →causes degradation and decreases the reliability of the brazed joint
66. more economically favorable
96. Figure 2 was modified in the revised manuscript.
102. RINT 2200 VF is the model of the XRD machine.
111. cutter
132-133. It has the sense to clarify here that the chemical composition data from XRF are presented as a plot →The chemical composition data obtained by XRF analysis are plotted in Figure 3.
18, 24, 79, 107, 138, 142, 218, 236, 246. As-electroplated →electroplated
162-163. The effect of the current density and deposition rate is described here, but the conclusion is not clear. →Therefore, the optimal current density is considered to be 2.0 A/dm2.
168-171. In addition, the figure caption of Figure 5 was modified in the revised manuscript.
174-176. The reviewer suggests clarifying those conditions also in chapter 3.3. →In order to make the audience understanding the information clearly. The recipe used for the deposition of Ni-11P layers for brazing tests was added to the figure caption of Figure 6.
193. (Fe, Ni, Cr) solid solution →Fe-Ni-Cr solid solution
221-223. Wu et al. [19] reported that the shear strength of a brazed joint with NiCrP filler metal increased from 36 MPa at 980 °C to 137 MPa at 1040 °C, i.e., the shear strength increased with the brazing temperature.
Point 2
224-225. suitable for what? How did the authors define that is suitable? Is there any declared limitation on the application of interest? Probably, it is easier to modify then expression.
Response 2
First of all, the brazed joint obtained in this study has excellent quality in terms of the absence of voids and flaws. On the other hand, although the BNi-6 (Ni-11P) filler metal has been commercially used in industrial applications, there is still little research on the shear strength of the brazed joint using it. However, some research on the shear strength of the brazed joint using BNi-2 or other Ni-based filler have been reported. For example, the shear strength of the brazed joint with BNi-2 filler was 100 MPa at 1040 °C; the shear strength increased from 36 MPa at 980 °C to 137 MPa at 1040 °C was obtained using NiCrP filler, i.e., the shear strength increased with the brazing temperature. The shear strength obtained in this study has a meaningful guiding role in practical applications for the brazing of the stainless steel using Ni-11P filler metal.
