呂1俳氏41 (課程博士(英文))Date of submission (month day year)

September 24小,2021

Department ofMechanicalStudenuD Number

ToshiakiYasuiSupervisors

en曾lneerlng

Pplicant's name

D179106

HiromiMiura

Nooririnah bintiomar

Abstract (Doctor)
Title ofThesis

Inauence ofsubstrate properties on Bonding Mechanism ofcold sprayed
Titanium Dioxide coating

Approx.80o words
Cold spraying is an emerging techniqLle in 、vhich spray material particles ranging from l t0 50μm
al'e stimulated by a stream of supersonic gas at a temperature belo、v ule materials melting point and leading to the production of the coating formation from the soHd state particles.1n term of thebonding mechanism for cold sprayed metal coating, the manifestation at the interface of adiabatic
Shear instability represents the most accepted bonding mechanism theory. Mean、Nhile, bonding
mechanism for cold sprayed pure ceramic materials is stiⅡ Unclear yet.
The substrate surface plays a cNcial role in achieving the hi8h・strength adhesiveness of coatings that are cold
Sprayed because their a田lesive strength is specifica11y determlned by the bonding of the first layer of Ti02Particles with the outermost surface ofthe substrate.1n addition, substrate 乳Ⅱ'face plays an lmportant role inthe deposition because it can provide chemical affinities durino the particle interaction after impact or plastic
deformation or thin layer remaining oxide. Literature on bonding mechanism of cold sprayed Ti020nto metal
Substrate has focused almost exclusively on Ti02 PO、vder properties and to date, no systematic investigation
has consjdel、ed 介om substrate properties perspective. The aim of this thesis is to study the factors andUnderstand the bonding mechanism that contributed from substrate hardness, substrate oxide surface

roughness and substrate oxidation in term of composition and thickness. substrate hardness have inauenced
toward substl'ate deformation 、Nhen cold sprayed Ti02 impacts the substrate surface with a high impact
Velocity. substrate deformation wi1Πead to mechanical anchoring which is one ofthe bonding mechanisms in
Cold spraying process. Roughness of the oxide surface can provide bonding mechanism through mechanicalinterlocking. As metalis used as substrate, a passive oxide layer with a thickness of a few nanometers wi11
Often make up the outermost surface. The increased temperature of the annealed substrate also indicatedthicker surface oxide on the surface of the substrate, and changes in the composition of the substrate.
Bonding mechanism by atomic intermixlng at a thin amorphous layer remaining about a fe、v nanometers
along the intel'face Ti02 Particle/newly form substrate surface due to chemical forces may also be thebonding mechanism involved in the cold spraying of titanium dioxide on metal surface. Thicker passive
Oxide on the surface of the substrate indicate a more inactive area to form the bonding between Ti02
Coating/newly formed surface of the substrate if thicker passive oxide remains on the substrate surface after
Cold sprayed Ti02 impacting. one of the bonding mechanisms is chemical reaction at the oxide・介ee intelface

between particles or particle/substrate that kno、Nn as metaⅡUrgical bonding.
I performed an experiment involving 5 types of materials as substrate, pure copper (CI020), pure aluminum(A1 105の, stainless steel (SUS304), P山'e chromium (cr) and structural steel (SS40の. selection of pureCopper and pure aluminum substrate because comprehensive analysis ofcold sprayed on copper substrate andaluminum substrate over a decade. This was basic understanding to study bonding mechanism of cold
Sprayed Ti02 0nto metal substrates. our research group's previous study sho、ved that 、vhen cold sprayedTi02 0nto preheating or anneaHng stainless steel a110y, the adhesion strength of Ti02 Coating showed anincreased trend butthis value was sti1110w compared to metal cold sprayed. To increase the adhesion strength
Of Ti02 Coatin8, bonding mechanism involved must be understood. selection of stainless steel, SUS 304 to

Clarify bonding mechanism involved, in order to increase the coating adhesion stl'ength. selection of pure
Chromium substrate to further understand the influence of chromium element in stainless steel substrate

to、vard bonding mechanism involved. Moreover, selection of structural steel, SS40o to study the inauence offerum element in stainless steel substrate.

My l'esearch findings sho、v that the adhesion strength of cold sprayed Ti02 Coatino on soft and pure annealed
materials, CI020 and A1 1050, showed a decreasing trend as the annealed substrate increased from room
temperature t0 400゜C. SUS 304 Showed increasing trend of cold sprayed Ti02 Coating as the tempel'ature of

the annealed substrate increased 介om room temperature t0 1000゜C. For pure cr, adhesion strength of Ti02
Coating sho、ved an lncreasing trend from room temperature t0 700゜c and decreased at looo゜C. Mean、vhile,the sS 40o sho、ved steadily an increased trend in the adhesion strength of Ti02 Coating from room
temperature to annealed 400゜c but no successful coating on annealed 700゜C SS 400.
Soft and pure annealed materials, CI020 and An 050 介om room temperature t0400゜C, decrease in hardness
is pronounced at 400゜c due to recrysta11isation. nB result shows substrate plastic deformation occurs on bothPure material at 400゜c but at this temperature the adhesion strength of the Ti02 Coatino is lo、vest. ThisSuggests that the bonding mechanism involved here is not mechanical anchoring. The TEM result showed aremaining thin alnorphous approximately lonm layer along the interface Ti02/metal substrate. As thetemperature of the annealed substrate increases, thicker surface oxide on the surface of the substrate but theParticle velocity is constant in a11 experiment condltion. Therefore, it contributes to more inactive area and itCould prevent cold sprayed Ti02 Coating from formin冬 bonding 、vith newly 介ee metal substrate oxide

Surface. MetaⅡUrgical bonding is pronounced as bonding mechanisln for both annealed soft and purematerials.

In the case ofannealed h雛d and a110ys material suS 304; annealed substrate hardness sho、Ned a decrease trend fromroom temperature t0 1000゜C. The nB result conflrmed substl'ate deformation occur on annealed looo゜C SUS 304
a丘er been impacted by high velocity cold sprayed Ti02. TEM flndings sho、ved a remaining thin amorphous layer
approximately lomη alona the interface Ti02/newly formed metal substrate for annealed looo゜C SUS304. Higher
temperature, such as looo゜C, mechanical and chemical factor affected the bonding mechanism by substrate
def01'mation and atomic intermixing. Moreover, SUS 304 from room temperature to annealed 700゜c sho、ved higher
annealed substrate hardness and no substrate deformation present. The only factor that inauenced bonding
mechanism is oxide layer on substrate surface. SUS 304 have oxide layer consist of Fe203 and cr203. Referring toresult ofpure chromium substrate showed steady increased ofcoating adhesion strength from RT to annealed 700゜Cbut structural steel, SS 40o on annealed 700゜C, no successful coating on this annealed substrate temperature.
Therefore, cr203 have major inauence to bonding mechanism of cold sprayed Ti02 0n stainless steel by mixedOxide bonding since our Ti02 PO、Nder feedstock have oxygen defective, Ti02Ⅸ. During the cold spraying process,the agglomerated powder ofTi02 in nano・scale primary particles,、 hich also contained nanoporosity, was fractured,
Ieaving an unstable surface with a dangling bond stl'ucture.The unstable surface Ti02Ⅸ With defective oxygen and adangling bond structure in the nano・scale primary particle, preferentia11y to form the chemical mixed、oxide bonding
Of Ti02‑Fe203+cr203. Kinetic spraying processes, including warm spray or cold spray, the pa11icle‑ substrate orParticle‑palticle interface is exposed to high temperature below the melting point and high compressive stressexceeding l‑2 Gpa at the impacted region. The combination of a thin amorphous phase of oxide, high temperatureand pressure, and strong reactivity oftitanium with oxygen could induce particle‑panicle bonding.
To sum up, our research had led us to substantial pr081'ess in clarifying the bonding mechanism assoclated

With cold sprayed ceramic materials. The present findings may help to clarify the role of remaining substrate
Oxide to bonding mechanism ofcold sprayed TI0?.