臺灣博碩士論文加值系統

本研究利用Nd-YAG雷射在壓鑄鋁合金A390表面以鎳基與鐵基的粉末進行雷射表面合金化的研究。粉末覆層利用電漿噴覆在A390鋁合金表面先形成附著於表面之披覆層，再經雷射重熔使披覆層與部分母材互混合成為表面合金化層並部分形成具有序排列之介金屬化合物，具有較好的耐磨耗耐腐蝕特特性。
本文在探討雷射參數組合與在鋁合金A390表面上的鎳基及鐵基合金化層的特性之間的關係，雷射參數主要為雷射功率及掃描速度。而因為雷射能量密度的分佈不一致性，造成合金化層之表面出現不連續性及未熔融的現象，降低雷射光斑直徑使得光束能量集中，得到表面完整熔融的表面，而硬化層特性包含硬化層內的硬度分佈、硬化層之幾何特徵 (硬化層之深度與寬度)，硬化深度與雷射功率大致成正比關係增加、且隨著掃描速與光束直徑的增加而減少。在多道次合金化層方面，硬度隨著合金化道次增加導致熱量累積而隨著下降。
由於鋁合金的高熱傳導係數以及快速的掃描速度，導致熔池能夠急速的冷卻，因此在A390鋁合金表面上形成淺的硬化層但是具有超過HV600以上的硬度值。在單道次鎳基合金化層中，存在著四種不同的微結構「針狀結構、雪花片狀結構、柱狀樹枝狀組織以及不規則塊狀物」，利用EDS及EPMA鑑定出前三者為Ni2Al3介金屬化合物而後者為NiAl介金屬化合物，然而在多道次鎳基合金化層中，也以XRD證明主要是形成針狀Ni2Al3以及不規則NiAl介金屬化合物。在硬度方面，NiAl介金屬化合物硬度較針狀Ni2Al3介金屬化合物高。在單道次鐵基合金化層中，微結構鑑定主要以胞狀樹枝狀Fe2Al5介金屬化合物以及不規則塊狀FeAl介金屬化合物為主，而因為多道次合金化製程導致母材與熔融粉末有較大的稀釋效果，因此富含鋁的針狀FeAl3介金屬化合物與富含鐵的不規則塊狀FeAl介金屬化合物以EDS及EPMA鑑定出分別形成於合金化層之上方與底部，而XRD、TEM以及SAD更加證明FeAl3以及FeAl介金屬化合物存在於多道次鐵基合金化層中。
利用SEM及OM觀察判斷鋁基材以及鐵基、鎳基合金化層經過磨耗測試後，分別為黏著磨耗（adhesive wear）以及擦損磨耗（abrasive wear），而鎳基合金化層之磨耗損失為鐵基合金化層之兩倍，故鐵基合金化層之磨耗抵抗能力優於鎳基合金化層，因此鐵基合金化層更能應用於延長磨耗元件之壽命。

Laser surface alloying with Ni- and Fe-based powder on the surface of squeeze casing A390 aluminum alloy was conducted utilizing Nd-YAG laser. Powder deposition on the surface of A390 Al alloy prior to laser alloying was carried out by using plasma-spraying method. Through laser remelting of the surface coating and the base metal the mixture of the coating and substrate will form an alloyed layer with compounds. The laser alloyed coating exhibits improved wear and corrosion resistance.
Relationship between laser processing parameters including laser power/scanning speed and the characteristics of Ni- and Fe-based alloyed layers on the surface of A390 Al alloy including hardness and geometrical features was investigated. Concentration of the beam energy by decreasing laser beam diameter would achieve completely molten surface. In general the hardened depth increased with increasing laser power and decreasing scanning speed. For multi-pass alloyed layer, the hardness decreases with increasing overlap between passes due to heat accumulation.
A shallow hardened layer with hardness value higher than HV600 on the surface of A390 Al alloy can be achieved. Four different microstructures such as acicular structure, snow-flake structure, columnar dendrite and irregular lump existed in the single-pass Ni-based alloyed layer. The former three microstructures were formed to be Ni2Al3 intermetallic compound and the last was NiAl intermetallic compound identified by EDS and EPMA. However, acicular Ni2Al3 and irregular-shaped NiAl compounds mainly formed in multi-pass Ni-based alloyed layer, which was identified by XRD results. The NiAl compound is much harder than Ni2Al3 compound The microstructure of single-pass Fe-based alloyed layer mainly consisted of cellular dendrite and irregular lump, which were identified as Fe2Al5 and FeAl compounds respectively. Due to overlap and higher dilution, the upper and bottom of the multi-pass Fe-based alloyed layer consisted of Al-rich needle-like structure and Fe-rich irregular lump, which were identified as FeAl3 and FeAl compounds respectively by EDS and EPMA. XRD results also revealed that FeAl3 and FeAl compounds indeed existed in the multi-pass Fe-based alloyed layer.
The adhesive wear of the Al substrate and the abrasive wear of Fe- and Ni-based alloyed layers was observed using SEM and OM. The wear loss of Ni-based alloyed layer was twice higher than that of Fe-based alloyed layer, indicating a superior wear resistance of Fe-based alloyed layer. Therefore, Fe-based alloyed layer could be applied in wear components to prolong the service life.

Table of content
Abstract.....................................................................................................Ⅰ
Acknowledgements…………………………………………………..... Ⅴ
Table of Contents………………………………………………………..Ⅵ
List of Tables……………………………………………………………Ⅸ
List of Figures……………………………………………………….......Ⅹ
Nomenclature………………………………………………………ⅩⅩⅡ
1. Introduction…………………………………………………...………1
2. Literature review………………………………………..............…....3
2.1. Laser surface hardening……………………………..……….3
2.2. Hardening by laser surface remelting…………..……………4
2.3. Metal matrix composite(MMC) strengthening by laser surface treatment on aluminum alloys…………………………...….5
2.4. Formation of intermetallic compound by laser surface alloying………..…………………………..………...………6
2.5. Wear behavior of aluminum alloys….……………..….……..9
2.6. Motivation………………………………………………….10
2.7. Objectives……………………………...………..…...……..11
3. The mechanisms of plasma-spray coating and laser surface alloying and wear of surface layer...................................................13
3.1. The mechanism of plasma-spray coating...…,,………………...13
3.2. Principles of plasma spraying…………..…………..………….15
3.3. The mechanism of laser surface alloying………………………18
3.4. Selections of alloying materials………………………...………28
3.5. Wear mechanisms………………………………………..……..29
3.5.1. Abrasive wear…………………………………….……..29
3.5.2. Adhesive wear…………………………..………….……33
3.5.3. Erosive wear…………………………………………….33
3.5.4. Surface fatique wear……………………………….……34
4. Experimental methodology……………..………………….……..35
4.1. Preparation of experimental materials and specimens…..….…...35
4.2. Experimental procedures……………………………….………..44
4.3. The determination of process parameters…………..…………....48
4.4. The analysis procedures……………………………………..…...55
4.5. Wear test………………………………………………………....56
4.5.1. Preparation of wear specimen and wear process…….…..56
4.5.2. Subsequent analysis……………………………………...58
5. Results and discussion
5.1. Microstructure analysis and hardness distribution of Ni-based plasma-sprayed coating with subsequent laser alloying…….…..59
5.1.1. Influence of laser power on single-pass laser alloyed layer...59
5.1.2. Influence of scanning speed on single-pass laser alloyed layer…………..……………………………………………62
5.1.3. Influence of scanning speed on multi-pass laser alloyed layer………………………………………………………..71
5.1.4. Microstructure, SEM/EDS, EPMA and XRD analyses of Ni-based alloyed layer……………………………………..87
5.2. Microstructure analysis and hardness distribution of Fe-based plasma-sprayed coating with subsequent laser alloying…...…..107
5.2.1. Influence of laser power on single-pass laser alloyed layer.107
5.2.2. Influence of scanning speed on single-pass laser alloyed layer…………………………………………………..…..112
5.2.2.1. Laser beam diameter 4.75mm…............................…...112
5.2.2.2. Laser beam diameter 3mm….................................…...119
5.2.3. Surface morphology and hardness distribution of multi-pass laser alloyed layer……................………..……………....127
5.2.4. Microstructure, SEM/EDS, EPMA and XRD analyses of Fe-based alloyed layer…….......................................……135
5.3. Wear characteristics and mechanisms……………….………...148
6. Conclusions and future work……….………………………..........164
Reference………………………………………………...……………167
LIST OF TABLES
Page
Table 4.1.1. Ni- and Fe-based alloys and compositions………………...32
Table 4.1.2. Compositions of A390 aluminum alloy…………....……....32
Table 4.3.1. The processing parameters in the laser treatment………….51
Table 4.5.1. Wear parameters of Fe- and Ni-based alloyed layer and Al substrate…………………………………………………..58
Table 5.1.1. EPMA results and stoichiometric ratio of needle-like structure, snow-flake structure, columnar dendrite and irregular structure in the single-pass Ni-based alloyed layer with 0.7 mm sprayed coating………………...…..100
Table 5.1.2. EPMA results and stoichiometric ratio of irregular lump in the multi-pass Ni-based alloyed layer with 0.7mm sprayed coating…………………….…………………………...106
Table 5.2.1. EPMA results and stoichiometric ratio of cellular dendrite and irregular lump in the single-pass Fe-based alloyed layer with 0.3mm sprayed coating......………………………...138
Table 5.2.2. EPMA results and stoichiometric ratio of irregular lump and needle-like structure in the multi-pass Fe-based alloyed layer with 0.3mm sprayed coating…………………..................145
Table 5.3.1. Comparison of wear resistance between the Al base metal, Fe-based alloyed layer and Ni-based alloyed layer............148
LIST OF FIGURES
Page
Fig. 3.1.1. Thermal spray techniques divided by their principal energy sources……………………………………………………..14
Fig. 3.1.2. Plasma spray techniques divided by their surrounding atomosphere………………………………………………..15
Fig. 3.2.1. Main plasma spray parameters controlled at presser levels…17
Fig. 3.2.2. The three stages of connected energy transfer process……...18
Fig. 3.3.1. stages involved in laser surface alloying from arrival of laser pulse to complete resolidification………………………….25
Fig. 3.3.2. (a) CW-CO2 laser-enlarge view shows melt trails overlapping to produce area coverage. (b) Pulse or Q-switched laser - enlarge view shows laser pulse raster scanned over surface to produce area coverage……………………………………..26
Fig. 3.3.3. (a) Framework of laser surface alloying gravitational self-feeding powder process. (b) Framework of laser surface alloying pre-placed powder process……………………….27
Fig. 3.5.1. Scheme of low-stress abration……………………………….32
Fig. 3.5.2. Scheme of high-stress abration………...................……........32
Fig. 4.1.1. Morphologies and sizes of Ni- and Fe-based alloy powders. (a)Morphology and size of Ni-based alloy powders. (b) Morphology and size of Fe-based alloy powders………….38
Fig. 4.1.2. Al-Si binary phase diagram………………………………….39
Fig. 4.1.3. Microstructure of A390 aluminum alloy…………………….39
Fig. 4.1.4. A390 specimen size………………………………………..40
Fig. 4.1.5. Main plasma spray devices(a) Controllable interface and powder-feeding machanery(b) Specimen holder, working table and plasma gun……………………………………………...41
Fig. 4.1.6. Rough surface morphology of Ni- and Fe-based plasma-sprayed layer.(a) Morphology of plasma-sprayed surface with the Ni-based alloy powder.(b) Morphology of plasma-sprayed surface with the Fe-based alloy powder…...42
Fig. 4.1.7. Hardness of as-sprayed layers is higher than that of the Al alloy substrat (HRB87). (a)Hardness distribution of the Ni-based sprayed layer. (b) Hardness distribution of the Fe-based sprayed layer……………………………………...43
Fig. 4.2.1. Nd-YAG Laser Processing System (a)Laser processing machinery………………………………………………….40
Fig. 4.2.1. Nd-YAG Laser Processing System (a)Laser processing machinery (b) Working table with X-Y axes and rotating axis…………………………………………………………45
Fig. 4.3.2. The schematic diagram showing location for microhardness test in the multi track……………………………….……...46
Fig. 4.3.3. Flow chart of experiment. (a) Laser surface alloying process. (b) subsequent analyses of the material test……..………….47
Fig. 4.5.1. Schematic illustration of the framework of the high temperature wear machine…………………………………57
Fig.4.5.2. The dimension of (a) specimen holder and (b) pin…..............57
Fig. 5.1. Appearance of 0.3mm Ni-based plasma-sprayed layer treated with various powers. (a) Laser treatment of 0.3mm Ni-based layer(b) Local magnification of alloyed passes……………....60
Fig. 5.1.2. Appearance of 0.7mm Ni-based plasma-sprayed layer treated
with various powers. (a) Laser treatment of 0.7mm Ni-based
layer(b) Local magnification of alloyed tracks……………...61
Fig. 5.1.3. Appearance of 0.3mm Ni-based plasma-sprayed layer treated
with various speeds. (a) Laser treatment of 0.3mm Ni-based
layer(b) Local magnification of alloyed passes......................63
Fig. 5.1.4. Appearance of 0.5mm Ni-based plasma-sprayed layer treated
with various speeds. (a) Laser treatment of 0.3mm Ni-based
layer(b) Local magnification of alloyed passes......................64
Fig. 5.1.5. Macrograph of 0.7mm Ni-based plasma-sprayed coating treated with various speeds. (a) Laser treatment of 0.7mm Ni-based layer. (b) Local magnification of alloyed passes…………………………………..…………………65
Fig. 5.1.6. Cross sections of various passes of Ni-based alloyed layer with prior sprayed coating thickness 0.3mm………………...….67
Fig. 5.1.7. Hardness Distribution of various passes of Ni-based alloyed layer with prior sprayed coating thickness 0.3mm………...67
Fig. 5.1.8. Cross sections of various passes of Ni-based alloyed layer with prior sprayed coating thickness 0.5mm……………………68
Fig. 5.1.9. Hardness Distribution of various passes of Ni-based alloyed layer with prior sprayed coating thickness 0.5mm...………68
Fig. 5.1.10. Cross sections of various passes of Ni-based alloyed layer with prior sprayed coating thickness 0.7mm………………69
Fig. 5.1.11. Hardness Distribution of various passes of Ni-based alloyed layer with prior sprayed coating thickness 0.7mm……...…69
Fig. 5.1.12. Macrograph of 0.3mm Ni-based plasma-sprayed coating treated with P=2000W, V=100mm/min, ΔX=1.5mm (a) Laser treatment of 0.3mm Ni-based layer. (b) Local magnification of position 1 and 2………………………72
Fig. 5.1.13. Macrograph of 0.3mm Ni-based plasma-sprayed coating treated with P=2000W, V=300mm/min, ΔX=1.5mm (a) Laser treatment of 0.3mm Ni-based layer. (b) Local magnification of position 1 and 2.………………………73
Fig. 5.1.14. Macrograph of 0.5mm Ni-based plasma-sprayed coating treated with P=2000W, V=100mm/min, ΔX=1.5mm (a) Laser treatment of 0.5mm Ni-based layer. (b) Local magnification of position 1 and 2 .……………………...74
Fig. 5.1.15. Macrograph of 0.5mm Ni-based plasma-sprayed coating treated with P=2000W, V=300mm/min, ΔX=1.5mm (a) Laser treatment of 0.5mm Ni-based layer. (b) Local magnification of position 1 and 2. ……………………...75
Fig. 5.1.16. Macrograph of 0.7mm Ni-based plasma-sprayed coating treated with P=2000W, V=100mm/min, ΔX=1.5mm (a) Laser treatment of 0.7mm Ni-based layer. (b) Local magnification of position 1 and 2. ……………………...76
Fig. 5.1.17. Macrograph of 0.7mm Ni-based plasma-sprayed coating treated with P=2000W, V=300mm/min, ΔX=1.5mm (a) Laser treatment of 0.7mm Ni-based layer. (b) Local magnification of position 1 and 2. ……………………...77
Fig. 5.1.18. Cross sectional view of multi-path alloyed layer treated on three kinds of Ni-based coating (0.3, 0.5, 0.7mm)with different scanning speeds (100 and 300 mm/min)…......…79
Fig. 5.1.19. Hardness distribution of multi-pass Ni-based alloyed layer with prior sprayed coating thickness 0.3mm (V=300 mm/min)……………………………………………...…...82
Fig. 5.1.20. Hardness distribution of multi-pass Ni-based alloyed layer with prior sprayed coating thickness 0.5mm (V=100 mm/min)…………………………………………………...83
Fig. 5.1.21. Hardness distribution of multi-pass Ni-based alloyed layer with prior sprayed coating thickness 0.5mm (V=300 mm/min)…………………………………………..………84
Fig. 5.1.22.Hardness distribution of multi-pass Ni-based alloyed layer with prior sprayed coating thickness 0.7mm (V=100 mm/min)…………………………………………...………85
Fig. 5.1.23.Hardness distribution of multi-pass Ni-based alloyed layer with prior sprayed coating thickness 0.7mm (V=300 mm/min)………………………………………...…………86
Fig. 5.1.24. Micrograph of single pass of Ni-based alloyed layer with prior sprayed coating thickness 0.7mm (P=2000W, V=200mm/min, d=3mm)……………….………………..87
Fig. 5.1.25. Local magnification of position 1 in the single-pass Ni-based alloyed layer with prior sprayed coating thickness 0.7mm (P=2000W, V=200mm/min, d=3mm)…………………......88
Fig. 5.1.26. Local magnification of position 2 in the single-pass Ni-based alloyed layer with prior sprayed coating thickness 0.7mm (P=2000W, V=200mm/min, d=3mm)……………………..88
Fig. 5.1.27. Local magnification of position 3 in the single-pass Ni-based alloyed layer with prior sprayed coating thickness 0.7mm (P=2000W, V=200mm/min, d=3mm)……………………..88
Fig. 5.1.28. Optical micrograph showing relationship between microhardness and distinct microstructure in the single-pass Ni-based alloyed layer with prior sprayed coating thickness 0.3mm (P=2000W, V=200mm/min, d=3mm)………….....89
Fig. 5.1.29. SEM/EDS analysis of needle-like structure in the single- path Ni-based alloyed layer with prior sprayed coating thickness 0.7mm…………………………………………………….91
Fig. 5.1.30. SEM/EDS analysis of snow-flake structure in the single- path Ni-based alloyed layer with prior sprayed coating thickness 0.7mm ……………………………………………………93
Fig. 5.1.31. SEM/EDS analysis of columnar dendrtic structure in the single-path Ni-based alloyed layer with prior sprayed coating thickness 0.7mm…………………………………96
Fig. 5.1.32. SEM/EDS analysis of irregular lump in the single-path Ni-based alloyed layer with prior sprayed coating thickness 0.7mm…………………………………………………….98
Fig. 5.1.33. Al-Ni binary phase diagram................................................100
Fig. 5.1.34. Optical micrograph of multi-path Ni-based alloyed layer with prior sprayed coating thickness 0.7mm. (2000W, 300 mm/min, d=3mm)………………………………………..102
Fig. 5.1.35. Optical micrograph showing two kinds of microstructures “needle-like structure and irregular lump” in the multi-path Ni-based alloyed layer with prior sprayed coating thickness 0.7mm. (2000W, 300mm/min, d=3mm)…… 102
Fig. 5.1.36. SEM/EDS analysis of needle-like structure in the multi- path Ni-based alloyed layer with prior sprayed coating thickness 0.73mm …………………………………………………103
Fig. 5.1.37. SEM/EDS analysis of irregular lump in the multi- path Ni-based alloyed layer with prior sprayed coating thickness 0.7mm…………………………………………………...105
Fig. 5.1.38. XRD spectrum of multi-path Ni-based alloyed layer with prior sprayed coating thickness 0.3mm............................106
Fig. 5.2.1. Macrograph of 0.3mm Fe-based plasma-sprayed coating treated with various powers. (300mm/min, d=4.75mm )(a) Laser treatment of 0.3mm Fe-based layer. (b) Local magnification of alloyed passes .…………….................109
Fig. 5.2.2. Macrograph of 0.5mm Fe-based plasma-sprayed coating treated with various powers. (a) Laser treatment of 0.5mm Fe-based layer. (b) Local magnification of alloyed passes…………………………………………………....110
Fig. 5.2.3 Macrograph of 0.7mm Fe-based plasma-sprayed coating treated with various powers. (a) Laser treatment of 0.7mm Fe-based layer. (b) Local magnification of alloyed passes...………………………………………………….112
Fig. 5.2.4. Macrograph of 0.3mm Fe-based plasma-sprayed coating treated with various speeds. (a) Laser treatment of 0.3mm Fe-based layer. (b) Local magnification of alloyed passes ..………………………………………………….114
Fig. 5.2.5. Macrograph of 0.5mm Fe-based plasma-sprayed coating treated with various speeds. (a) Laser treatment of 0.5mm Fe-based layer. (b) Local magnification of alloyed passes ...……………………………………………........115
Fig. 5.2.6. Macrograph of 0.7mm Fe-based plasma-sprayed coating treated with various speeds. (a) Laser treatment of 0.7mm Fe-based layer. (b) Local magnification of alloyed passes …..……………………………………………….116
Fig. 5.2.7. Cross sections of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.3mm……………………118
Fig. 5.2.8.Hardness Distribution of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.3mm…….…..117
Fig. 5.2.9. Cross sections of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.5mm……………...…….118
Fig. 5.2.10. Cross sections of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.7mm……………..118
Fig. 5.2.11. Macrograph of 0.3mm Fe-based plasma-sprayed coating treated with various speeds. (a) Laser treatment of 0.3mm Fe-based layer. (b) Local magnification of alloyed passes…………………………………………………..121
Fig. 5.2.12. Macrograph of 0.5mm Fe-based plasma-sprayed coating treated with various speeds. (a) Laser treatment of 0.5mm Fe-based layer. (b) Local magnification of alloyed passes ………...………………………………………..122
Fig. 5.2.13. Macrograph of 0.7mm Fe-based plasma-sprayed coating treated with various speeds.(d=3mm) (a) Laser treatment of 0.7mm Fe-based layer. (b) Local magnification of alloyed passes …………………………………………123
Fig. 5.2.14. Cross sections of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.3mm (P=2000W, d=3mm)………………………...……………………….124
Fig. 5.2.15. Hardness Distribution of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.3mm (P=2000W, d=3mm)…………………………………………………..124
Fig. 5.2.16. Cross sections of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.5mm (P=2000W, d=3mm)………………………………………………..125
Fig. 5.2.17. Hardness Distribution of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.5mm (P=2000W, d=3mm)…………………………………………………..125
Fig. 5.2.18. Cross sections of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.7mm (P=2000W, d=3mm)………………………………………………….126
Fig. 5.2.19. Hardness Distribution of various passes of Fe-based alloyed layer with prior sprayed coating thickness 0.7mm (P=2000W, d=3mm)…………………………………………………126
Fig. 5.2.20. Macrograph of 0.3mm Fe-based plasma-sprayed coating treated with P=2000W, V=400mm/min, ΔX=1.5mm (a) Laser treatment of 0.3mm Fe-based layer. (b) Local magnification of position 1 and 2. .…………..………..128
Fig. 5.2.21. Macrograph of 0.5mm Fe-based plasma-sprayed coating treated with P=2000W, V=400mm/min, ΔX=1.5mm (a) Laser treatment of 0.5mm Fe-based layer. (b) Local magnification of position 1 and 2.. ………….………...129
Fig. 5.2.22. Macrograph of 0.7mm Fe-based plasma-sprayed coating treated with P=2000W, V=400mm/min, ΔX=1.5mm (a) Laser treatment of 0.7mm Fe-based layer. (b) Local magnification of position 1 and 2. …………...………..130
Fig. 5.2.23. Cross-sectional view and hardness distribution of multi-pass Fe-based alloyed layer with prior sprayed coating thickness 0.3mm (P=2000W, V=400mm/min, d=3mm, ΔX=1.5 mm)……………………………………………………….132
Fig. 5.2.24. SEM showing surface morphology of multi-pass Fe-based alloyed layer with prior sprayed coating thickness 0.5mm (P=2000W, V=400mm/min, d=3mm, ΔX=1.5mm) with many cracks……………………………..……………..133
Fig. 5.2.25. SEM showing surface morphology of multi-pass Fe-based alloyed layer with prior sprayed coating thickness 0.7mm (P=2000W, V=400mm/min, d=3mm, ΔX=1.5mm) with many cracks……………………..………………………134
Fig. 5.2.26. Micrograph showing the transverse morphology with irregular lump and cellular dendrite in the single-pass Fe-based alloyed layer with prior sprayed coating thickness 0.3mm……………………………………….136
Fig. 5.2.27. Micrograph showing microhardness marks on different microstructures such as the irregular lump and cellular dendrite………………………………………………...136
Fig. 5.2.28. Results of SEM/EDS analysis of the cellular dendrite in the single-path Fe-based alloyed layer with prior sprayed coating thickness 0.3mm………………….………………………137
Fig. 5.2.29. Results of SEM/EDS analysis of irregular lump in the single-path Fe-based alloyed layer with prior sprayed coating thickness 0.3mm………......................................138
Fig. 5.2.30. Fe-Al binary phase diagram[45]………………………….139
Fig. 5.2.31. Optical micrograph of overall multi-path Fe-based alloyed layer with prior sprayed coating thickness 0.3mm (P=2000W, V=400mm/min, d=3mm, Δ X= 1.5mm)…141
Fig 5.2.32. Optical micrographs of microhardness marks on irregular lump and needle-like structure………………………….141
Fig. 5.2.33. Results of SEM/EDS analysis of irregular lump in the multi-path Fe-based alloyed layer with prior sprayed coating thickness 0.3mm (P=2000W, V=400mm/min, d=3mm, Δ X= 1.5mm)…………………..…………….142
Fig. 5.2.34. Results of SEM/EDS analysis of needle-like structure in the multi-path Fe-based alloyed layer with prior sprayed coating thickness 0.3mm (P=2000W, V=400mm/min, d=3mm, Δ X= 1.5mm)………...……………………….143
Fig. 5.2.35. Fe-Cr binary phase diagram. [45]………………………...143
Fig. 5.2.36. XRD result of multi-path Fe-based alloyed layer with prior sprayed coating thickness 0.3mm (P=2000W, V=400mm/min, d=3mm, Δ X= 1.5mm)………………………………..…144
Fig. 5.2.37. Structure characteristics of α-Al in the Fe-Al alloy layer: (a) TEM morphology (x60000) (b) electron diffraction pattern……………………………………………………147
Fig. 5.2.38. Structure characteristics of FeAl in the Fe-Al alloy layer: (a) TEM morphology (x130000) (b) electron diffraction pattern………………………………………………….....147
Fig. 5.2.39. Structure characteristics of amorphous phase in the Fe-Al alloy layer:(a) TEM morphology(x110000) (b) electron diffraction pattern…………………………………….......147
Fig. 5.3.1. SEM/EDS results of the surface of Ni-based alloyed layer with prior sprayed coating thickness 0.7mm before wear test…………………………………………………….……149
Fig. 5.3.2. SEM/EDS results of the surface of Fe-based alloyed layer with prior sprayed coating thickness 0.3mm before wear test………………………………………………………….150
Fig. 5.3.3. Temperature history of the Al substrate, Fe-based alloyed layer and Ni-based alloyed layer during wear test………………152
Fig. 5.3.4. The friction coefficient of the Al substrate, Fe-based alloyed layer and Ni-based alloyed layer during wear test…….....153
Fig. 5.3.5. Optical micrographs of wear surface morphology of the Al substrate, Fe-base alloyed layer with prior sprayed coating thickness 0.3mm, Ni-based alloyed layer with prior sprayed coating thickness 0.7mm and their counter pins after wear test…………………………………….………………….155
Fig. 5.3.6. SEM/EDS results of the wear surface of the Fe-based alloyed layer with prior sprayed coating thickness 0.3mm after wear test………………………………………………………...157
Fig. 5.3.7. SEM/EDS results of the wear debris of the Fe-based alloyed layer with prior sprayed coating thickness 0.3mm after wear test……………………………………………………….....158
Fig. 5.3.8. The wear surface of the Fe-based alloyed layer after wear test showing the material detachment and crack initiation…….159
Fig. 5.3.9. SEM/EDS results of the wear surface of the Ni-based alloyed layer with prior sprayed coating thickness 0.7mm after wear test…………………………………………………………161
Fig. 5.3.10. SEM/EDS results of the wear debris of the Ni-based alloyed layer with prior sprayed coating thickness 0.7mm after wear test………………………………………………………..162
Fig. 5.3.11. The worn surface of the Ni-based alloyed layer after wear test showing the material detachment and crack initiation…...163
NOMENCLATURE
d : laser beam diameter
k : thermal conductivity
p : laser power
T : temperature
T0 : room temperature
Tm : melting temperature
V : scanning velocity
ρ : density

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